Hayes began his career with the heavy metal band Wretch. Later he was a founding member of the Progressive Heavy Metal band Castle Black with other former members of Wretch, Nick Giannakos (Lead Guitar) and Drummer, Jeff Currenton. It was during this time where he began a long association with Tim "Ripper" Owens, as Castle Black and Winter's Bane often played the same venues around Northeastern Ohio. Hayes eventually was offered, and accepted, membership in Winter's Bane. Both Hayes and Owens performed on Winter's Bane's 1993 debut album Heart of a Killer. Dennis also played in the Heavy metal band Seven Witches from 2004 to 2005, but left to form Beyond Fear together with Owens, a side project to the singer's role in Iced Earth.
After James "Bo" Wallace left Iced Earth in March 2007, Hayes was called in to replace him on the band's upcoming tour. Following Owens' departure from Iced Earth later that year, Hayes also left the band.