Ah, you mean in contrast to the fire-breathing ants from FO3?
Not to mention the centaurs... honestly, considering what Fallout has already shown us, I see no problem with them, and besides, we don't even know what they are or how they came to be, there could be an explanation for them in the game for all we know.
Although I will make one small criticism about their design, namely that they do not look like something that a name like "nightstalker" would make me think of. When you give a creature a name like that, it invokes a certain image, for one thing, I expect it to be something nocturnal, yet the screenshots showing them are obviously in daylight.
Another description of chupacabras, although not as common, describes a strange breed of wild dog. This form is mostly hairless and has a pronounced spinal ridge, unusually pronounced eye sockets, fangs, and claws. It is claimed that this breed might be an example of a dog-like reptile. Unlike conventional predators, the chupacabras is said to drain all of the animal's blood (and sometimes organs) usually through three holes in the shape of an upside-down triangle or through one or two holes.
I don't know, I don't see any evidence that they drain the blood of their pray, but of course, it's possible that they do for all we know, considering how little unformation we have on them.