Technically yes DNS allows multiple PTR RRs to be returned for a single query. However the General Consensus from the DNS types (search an archive of comp.protocols.dns.bind, for example here or here; look enough and you'll see threats to put together a "Best Practices" comdemnation of it) is still that you shouldn't do that because pretty much everything is written with the expectation that PTRs map to a single A record. There's also the problem that it's possible (with a sufficiently hostname-ful IP) to have more PTR RRs than can be returned in a single UDP packet. And I can't say that I've personally ever seen it happen in the wild in 15+ years of varying degrees of sysadmining.

Sure, you can do it; you can also use a pickaxe to poke speed holes in your car's hood. Neither of them really are going to be of much practical benefit.