What would happen if you hack a Shedinja with belly drum? Would it Faint, or lose no HP? My wifi is down unfortunately so I cannot check.
I guess that would be the reason he can not learn Belly-drum. I would assume it would fail like Substitute does. Source: Logical reasoning that because Substitute fails so would any other status move that lowers/raises hp. Source for the substitute thing: Bulbapedia
Source for knowing he can not learn Belly-drum: I looked it up