I don't know if Kevin Bloody Wilson has ever sung If God Smoked Cannabis, but he certainly didn't write it. It was written by Bob Rivers and has been sung by a few people, including Joan Osborne herself.
I haven't kept up with KBW in recent years, but he was more about funny originals than parodies when I was a fan in the 80s and 90s. The only parodies I can remember him doing are I Knew The Bride (When She Used to be a Moll) and Living Next Door to Alan (warning - would not pass muster on current attitudes to race). But there may be some other parodies that I missed.
Kev is definitely an Aussie legend though. I haven't listened to him in years but I'm still nearly word-perfect on You Orta See Me When I'm Pissed.