There is various debates about the scrum wheeling and then they may be the hindmost player, but it's few and far between that happens, and if it does chances are your scrums are having more issues than just that.
I've never seen a proper move where the ball is put to a wing forward and then deliberately wheeled so that they are at the back, and then they pick it up.
If no No8 in senior game it is possible they may deliberately wheel so as to put a flanker hindmost and do a pickup move. As Crossref says however if its a plan they'll probably pack a No 8... however just because something is usual doesn't mean the unusual cannot happen
Mind you with 1 down in the scrum they'd be better advised to try and keep it straight. Agree with Robbie this far, it would be unusual.
It's more likely that the opposition are wheeling trying for a turnover or simply to destabilise. But the wheel may well put a flanker as hindmost player, and he is perfectly entitled to break bind and pick up