Yeah absolutely. That's really the crux of the issue. He was expelled, and if he has to provide an explanation why (or his school does) it could get messy. Does it say "expelled for violation of school rules" or "expelled for a drug related incident" or what? But he has no criminal record (to my knowledge) and this wasn't any sort of legal matter. It's like how punching your brother might get you a spanking from your parents, but that's way different than punching him at a bar and getting arrested for assault by a cop.
There's a lot of variables we don't know. That's all I'm really getting at. The expulsion alone is a HUGE hurdle but I don't really know how much this whole thing about "dealing" is overblown. There is no record of it, none of us know the details/extent, and I think any reasonable person would conclude he's not some drug kingpin.
What if he has a 4.0 GPA at his new school, is an overall good egg, and the blemish is the expulsion for an obfuscated reason? I could see a lot of wiggle room on that. Certainly there are a lot of schools still actively recruiting him.