I think we should wait for confirmation before we pass that idea around. Some musicians I'd put that as a strong possibility, but I've never really seen mention of their being any drug issues amongst the Slipknot/Stone Sour crew. Then again, there could be zero issues, and then there is a first.
But regardless of drug use, people do drop dead out of the blue.
It's always possible drugs were involved, but he seems to at least made an attempt to appear clean, considering the only thing the media has ever reported was a 2003 DUI and Possession (coke and weed).