Question: Are Danie Visser and Bob Bryan both professional tennis players?

Context articles: Danie Visser
Athletic DNA
Association of Tennis Professionals
Donald Dell
Challenge of Champions
Vera Zvonareva
Virginia Slims Circuit
1968 Wimbledon Championships – Men's Singles
Bob Bryan
1991 ATP German Open – Doubles

Danie Visser (born 26 July 1961) is a former professional tennis player from South Africa.
 A doubles specialist, he won 3 Grand Slam men's doubles titles (2 Australian Open and 1 US Open).
 Visser reached the World No. 1 doubles ranking in January 1990.
Athletic DNA (ADNA) is an American sports apparel company.
 Founded in Seattle in 2007, ADNA began by training young tennis athletes, which evolved into sponsoring Select Junior Tennis players, and then expanded to manufacturing clothing for youth and adult tennis players.
 ADNA has since spread to professional tennis, and currently sponsors players on the ATP Tour & WTA Tour.
The Association of Tennis Professionals (ATP) was formed in September 1972 by Donald Dell, Bob Briner, Jack Kramer, and Cliff Drysdale to protect the interests of male professional tennis players.
 Drysdale became the first President.
 Since 1990, the association has organized the worldwide tennis tour for men and linked the title of the tour with the organization's name.
 In 1990 the organization was called the ATP Tour, which was renamed in 2001 as just ATP and the tour being called ATP Tour.
 In 2009 the name was changed again and is now known as the ATP World Tour.
 It is an evolution of the tour competitions previously known as Grand Prix tennis tournaments and World Championship Tennis (WCT).
Donald Dell (born June 17, 1938 in Savannah, Georgia, United States) is an attorney and was a professional tennis player, U.S. Davis Cup captain, and administrator.
 Dell was one of the first professional sports agents, having represented professional tennis players Arthur Ashe, Stan Smith, Jimmy Connors, and Ivan Lendl during pro tennis' golden age (1975 to 1985).
 He was also the founder of Professional Services (ProServ), one of the nation's first sports marketing firms established in 1970 with co-founder, Frank Craighill, a fellow law partner.
 His younger brother, Dick, worked for ProServ managing US Open champion Gabriela Sabatini, and played Number One Singles for the University of Michigan.
 He was Big Ten #1 Singles Champion in 1969.
The "Challenge of Champions" was created to be one of the richest prize money tennis events in the world.
 Created by Leo E. Fenn III in 1985 as an Invitation Only Tennis Tournament which would feature daily matches which were the equivalent to the Finals of the US Open or Wimbledon.
 It was usually held before the Masters and invited only the top eight men's tennis players in the world according to their rankings on the ATP poll.
 In 1985, creator & founder 24-year-old Leo E. Fenn III partnered with 28-year-old Mark Myden to form a company called Special Events Productions.
 SEP produced the "Challenge of Champions" Tournament which became a major player in professional tennis.
 These two entrepreneurs became the youngest producers in history of professional tennis.
 Leo & Mark acquired major fortune 500 corporate sponsors such as AT&T, VISA, Cadillac, Fila Sportswear, DeBeers Diamonds as well as negotiated two days of live weekend television coverage on NBC.
 Their title sponsorship package sold to AT&T was the largest single vent sponsorship package in professional tennis that year.
 Leo negotiated with the brand new Thomas Mack Center Arena in Las Vegas to host the inaugural event.
 The event rights were eventually sold to Pro Serve and concluded following the 1989 Challenge.
Vera Igorevna Zvonareva (Russian: Ве́ра И́горевна Звонарёва ; ] ; born 7 September 1984) is a Russian professional tennis player.
 She was introduced to tennis at the age of six and turned professional in 2000.
 Her career high is world No. 2 by the WTA.
 Zvonareva has won twelve WTA Tour singles titles and reached the finals of the 2008 WTA Tour Championships, 2010 Wimbledon Championships, and 2010 US Open.
 She also was a bronze medalist at the 2008 Beijing Olympics.
 In doubles, she has won four Grand Slam titles.
 Two of the titles came in women's doubles, the first one at the 2006 US Open, partnering Nathalie Dechy, and the other at the 2012 Australian Open, partnering Svetlana Kuznetsova.
 Her other two came in mixed doubles, the first at the 2004 US Open, partnering Bob Bryan, and her second at the 2006 Wimbledon Championships, partnering Andy Ram.
The Virginia Slims Circuit was a tennis tour consisting of a group of originally nine female professional players.
 Formed in 1970, the Virginia Slims Circuit eventually became the basis for the later named WTA Tour.
 The players, dubbed the "Original 9", rebelled against the United States Lawn Tennis Association (USLTA) due to the wide inequality between the amount of prize money paid to male tennis players and to female tennis players.
Rod Laver defeated Tony Roche 6–3, 6–4, 6–2 in the final to win the Gentlemen's Singles title at the 1968 Wimbledon Championships.
 It was Laver's third Wimbledon title, and his seventh grand slam overall.
 This was the first year when professional tennis players were allowed to compete at the Wimbledon Championships.
 Previously only amateur tennis players could compete.
Robert Charles Bryan (born April 29, 1978) is an American male professional tennis player.
 He has won twenty-three Grand Slam titles: 16 in men's doubles and 7 in mixed doubles.
 He turned professional in 1998.
 With his twin brother Mike, he has been world No. 1 doubles player for much of the last several years, first achieving the top ranking in September 2003.
 The brothers were named ATP Team of the Decade for 2000–2009.
 The brothers became the second men's doubles team to complete the career golden slam at the 2012 Summer Olympics.
The 1991 German Open was a tennis tournament played on outdoor clay courts and was part of the ATP Super 9 of the 1991 ATP Tour.
 It took place at the Rothenbaum Tennis Center in Hamburg, Germany, from May 6 through May 13, 1991.
 Sergio Casal and Emilio Sánchez won in the final against Cássio Motta and Danie Visser, 7–6, 7–6.