Question: Were Mariaan de Swardt and Ken Rosewall both professional tennis players?

Context articles: 1998 Boston Cup – Singles
Ken Rosewall
Gonzales–Rosewall rivalry
1997 Challenge Bell – Doubles
1998 Boston Cup – Doubles
Mariaan de Swardt
1997 Welsh International Open – Doubles
1996 Toray Pan Pacific Open – Doubles
2000 Australian Open – Mixed Doubles
1999 Wimbledon Championships – Women's Doubles

Mariaan de Swardt won in the final 3–6, 7–6, 7–5 against Barbara Schett.
Kenneth Robert Rosewall {'1': ", '2': ", '3': 'AM, MBE', '4': "} (born 2 November 1934) is a former world top-ranking amateur and professional tennis player from Australia.
 He won a record 23 tennis Majors including 8 Grand Slam singles titles and before the Open Era a record 15 Pro Slam titles and a record 35 Major finals overall.
 He won the Pro Grand Slam in 1963.
 Rosewall won 9 slams in doubles with a career double grand slam.
 He is considered to be one of the greatest tennis players of all time.
 He had a renowned backhand and enjoyed a long career at the highest levels from the early 1950s to the early 1970s.
 Rosewall was one of the two best male players for about nine years and was the World No. 1 player for a number of years in the early 1960s.
 He was ranked among the top 20 players, amateur or professional, every year from 1952 through 1977.
 Rosewall is the only player to have simultaneously held Pro Grand Slam titles on three different surfaces (1962–1963).
 At the 1971 Australian Open he became the first male player during the open era to win a Grand Slam tournament without dropping a set.
American tennis player Pancho Gonzales had a long-running rivalry with Australian Ken Rosewall.
 Gonzales is still sometimes considered to be a candidate for the greatest tennis player of all time; he was the dominant player of the 1950s and still holds the men's all-time record of being ranked world No. 1 for eight years.
 Rosewall became the world's best player upon Gonzales's semi-retirement in 1961 and held that position either by himself or sharing it with others for six years.
 Rosewall was signed in 1956 by the promoter Jack Kramer, a former #1 player himself, to join his small band of touring professionals in 1957.
 He then engaged in a round-the-world, head-to-head tour against Gonzales, the defending world's champion, over the next five months, winning 26 matches but losing 50.
 In his 1979 autobiography Kramer included both Gonzales and Rosewall in his list of the 21 greatest players of all time.
 Kramer, however, initially "panicked" upon signing Rosewall.He was a cute little fellow with a dink serve, who operated mostly from the baseline.
 That great volley of his hadn't been developed yet.
 I was afraid that Gorgo would eat him alive and put us out of business the rest of the way.
 But like a lot of people I completely underestimated Rosewall.
 Before their opening match in Melbourne, Kramer went to Gonzales and asked him to "carry" Rosewall, giving him a better share of the gate to gain his assent.
 Gonzales did try to carry out his part of the deal for a few matches, but then called it off, telling Kramer that he was no longer able to play his normal game.
 Kramer agreed.
 "It was... obvious that Rosewall was not the pushover I had feared.
 (In fact, Gonzales only beat him 50–26, and it was always competitive.)"
 Six years older than Rosewall, 13 years later, in 1970, Gonzales defeated him in 6–4, 6–4, in the 199th and next-to-last match they ever played—Gonzales was 42 years old at the time and Rosewall was considered to be the co-No.
 1 player in the world.
Debbie Graham and Brenda Schultz-McCarthy were the defending champions, but decided not to compete together.
 Graham partnered with Mariaan de Swardt, but lost in the semifinals to Alexandra Fusai and Nathalie Tauziat.
 Schultz-McCarthy partnered with Rebecca Jensen, but lost in the first round to Patricia Hy-Boulais and Chanda Rubin.
Lisa Raymond and Rennae Stubbs won in the final 6–4, 6–4 against Mariaan de Swardt and Mary Joe Fernández.
Mariaan de Swardt (born 18 March 1971) is a former tennis player from South Africa, who played as a professional from 1988 to 2001.
 She twice represented her native country at the Summer Olympics, in 1992 and 1996, and was a member of the South African Fed Cup Team in 1992 and 1994–1997.
 In 2006, de Swardt became a U.S. citizen.
Katrina Adams and Mariaan de Swardt were the defending champions but did not compete that year.
Gigi Fernández and Natasha Zvereva were the defending champions and won in the final 7–6, 6–3 against Mariaan de Swardt and Irina Spîrlea.
Mariaan de Swardt and David Adams were the defending champions but only Adams competed that year with Kristie Boogert.
The 1999 Wimbledon Championships – Women's Doubles was the women's doubles event of the hundred-and-thirteenth edition of Wimbledon, the third Grand Slam of the year, the most prestigious tournament on grass courts, and the oldest tennis tournament in the world.
 Martina Hingis and Jana Novotná were the defending champions but only Novotná competed that year with Natasha Zvereva.
 Novotná and Zvereva lost in the semifinals to Mariaan de Swardt and Elena Tatarkova.