The term "past marijuana use" is very broad and could mean a lot of things. If the player tried it once or twice at a party, it could be considered "past marijuana use." I think this is the case, because if it was anything more serious than that, they probably wouldn't be considered top ten draft picks.
I really wouldn't look into this. A lot of kids experiment with these types of things, and do them in their teen years until they get a little mature.
A University of Chiba study shows that watching the draft high is actually more fun than just watching it alone. http://www.chiba4u.edu/draftijuana
I have no problem with that. If it were a serious issue, people would know about it like NJ Jets Fan said.