Not to be confused with a certain other neanderthal
The Neandors, also known as Homo Sapien Hyannothus, is a recognized strain of Abhuman within the Imperium. They are restricted to the world of Hyannoth IV. As you can imagine, these guys don't really live up to the imagination now ain't it. They are fucking Neanderthals or whatever cavemen caricatures you can think off.
They are on equal terms of Pelagers when it comes to fluff, as we don't really know that much about them other than the fact that they are cavemen. So possibly, they are dumb but physically strong, tough and broad. So for all intents and purposes, a mixture between a Squat and an Ogryn. They don't really feature that much in the Imperium's fluff and they might as well be petting zoos for the normal Humans to gawk at.
But hey, for all their faults and fluff vagueness, they are at least better represented than the Troths.
If you want to play some of these guys or use them as a model. You could basically glue a Space Wolves' bearded head on an Imperial Guard (probably Catachan) body. They are already viewed as barbarians anyway, so it won't break the fluff. That or use the heads of Ogryns as a stand-in Proxy for the same brutish and simple-minded look.