Short Answer: Yes, I'd say they are.
Long Answer: While it's kinda debatable, I'd say they are. Firstly, they have all the characteristics of one: they have moves, abilities, and types, they can be caught in a ball, yada yada. If they weren't Pokemon, then none of that would really apply. Secondly, they never have any function outside of being Pokemon: while its true that they have the whole post-game side quest, we never see them in the overworld knocking down buildings or whatever. Nope, they're there to be caught. And its true that their designs are very strange, but that can be owed them being Pokemon from Ultra Space, where everything is all weird and crazy. So, because of all of this... see the short answer, I guess!
Hope I was able to help!