According to the fantasy updates on cbssports.com, he can serve the suspension on the DL and this won't impact anything as far as his return...
"Volquez was a potential second-half contributor in Fantasy and this news likely won't keep him from reaching his late July or early August return date, since he can serve the suspension while on the DL. He was reportedly ahead of schedule and could return shortly after the All-Star break. He remains a must-stash in deeper leagues with DL spots still. He could be a dominant Fantasy arm during crunch time down the stretch." - Cbssports.com