That question and other anecdotes from the European Tour perspective are answered by Steve Elling who quotes several players talking about Vijay Singh's admission to using a banned substance.
Lee Westwood was the funniest:
"Deer-antler spray?" Westwood said, repeating the offending substance. "Sounds like something you'd wax your car with."
This from Euro Tour head George O'Grady answers whether Singh could play overseas during his ban:
"This, a drug thing, if that's what it was, whatever the PGA Tour would do, we would support," O'Grady said.