He's never actually been implicated, no, but there's a ton of circumstantial evidence.
This is what he looked like when he came up in 1989:
And this was him in 1996:
Now, could he have just hit the gym a lot? Of course. But the fact of the matter is that most anyone in that era who saw a prodigious, and overnight, increase in power (be it a power arm, or a power bat) has a cloud of suspicion over them.