Question: Are Andrew Stockdale and Sully Erna both vocalists?

Context articles: Sully Erna
Andrew Stockdale
Meliah Rage
Keep Moving (EP)
Hollow (Godsmack song)
Keep Moving (Andrew Stockdale album)
Wolfmother
Lisa Guyer
Godsmack discography
Avalon (Sully Erna album)

Salvatore Paul "Sully" Erna Jr. (born February 7, 1968) is the American vocalist and guitarist for the American hard rock band Godsmack.
 He is also a harmonica player, percussionist and pianist, performing these on albums and at live shows.
 He was ranked 47th in the Top 100 Heavy Metal Vocalists by "Hit Parader".
Andrew James Stockdale (born 20 July 1976) is an Australian rock musician, singer and songwriter best known as the lead vocalist, lead guitarist and only mainstay member of the rock band Wolfmother, which formed in 2000.
 In 2007, alongside his Wolfmother bandmates, he won 'Songwriter of the Year' at the APRA Awards.
 Aside from his work with Wolfmother, Stockdale was featured on the 2010 single "By the Sword" by Slash.
Meliah Rage are an American power metal band from Boston, formed in 1987 by guitarist/songwriter Anthony Nichols.
 They are characterized primarily as thrash metal with more classical metal melodies.
 The band has released seven albums.
 Its current members includes Anthony Nichols, Jim Koury, Darren Lourie, Marc Lopes and Stu Dowie.
 They at one time featured Godsmack front man Sully Erna on drums, who appeared on the Unfinished Business LP.
Keep Moving is the debut solo extended play (EP) by Australian musician Andrew Stockdale.
 Recorded throughout 2012 and 2013 in Byron Bay, the EP features four songs from Stockdale's upcoming debut solo album of the same name.
 It was released by Universal on 26 April 2013 in Australia, Germany and Austria, on 28 April in the United Kingdom and the rest of Europe, and on 30 April in the United States.
"Hollow" is an acoustic song by the heavy metal band Godsmack from their fourth studio album, "IV".
 Frontman Sully Erna and Lisa Guyer are on the song vocals.
 "Hollow" is the only acoustic song that appeared in the album, and Erna has played it frequently on his solo tour.
Keep Moving is the debut solo studio album by Australian hard rock musician Andrew Stockdale.
 Initially conceived as the third album by Stockdale's band Wolfmother, it was later announced to be a solo album after the disbandment of the group in March 2013.
 Recorded by Wolfmother between 2011 and 2013, "Keep Moving" was released by Universal in June 2013.
Wolfmother are an Australian hard rock band from Sydney, New South Wales.
 Formed in 2000 by vocalist and guitarist Andrew Stockdale, bassist and keyboardist Chris Ross and drummer Myles Heskett, the group currently includes Stockdale, bassist and keyboardist Ian Peres and drummer Hamish Rosser.
 Wolfmother released their self-titled debut album "Wolfmother" in Australia in 2005 and internationally in 2006.
 The album reached number 3 on the Australian Albums Chart and the top 40 in the US and the UK, and has to date sold over 1.5 million copies worldwide.
Lisa Guyer is an American singer, guitarist, and songwriter.
 She was born into a musical family that put on shows in their community, and Guyer learned to sing and dance by age four.
 Guyer's vocal skills are completely self-taught.
 Godsmack's Sully Erna describes Guyer as having "a phenomenal voice and a four-octave range.
 Guyer is an associate professor at Berklee College of Music in Boston.
Godsmack is an American alternative metal band founded in 1995 by singer Sully Erna and bassist Robbie Merrill.
 The band has released six studio albums, one EP, one compilation, three video albums, and twenty-three singles.
 Erna and Merrill recruited local friend and guitarist Lee Richards and drummer Tommy Stewart to complete the band's lineup.
 In 1996, Tony Rombola replaced Richards, as the band's guitarist.
 In 1998, Godsmack released their self-titled debut album, a remastered version of the "All Wound Up" demo.
 The album was distributed by Universal/Republic Records and shipped four million copies in the United States.
 In 2001, the band contributed the track "Why" to the Any Given Sunday soundtrack.
 After two years of touring, the band released "Awake".
 Although the album was a commercial success, it failed to match the sales of "Godsmack".
 In 2002, Stewart left the band due to personal differences, and was replaced by Shannon Larkin.
Avalon is the first solo studio album by American rock musician Sully Erna, released on September 14, 2010.
 "Avalon" is a combination of work that took Sully Erna almost seven years to complete.