They are the same genus, and most likely quite compatible...a fair amount of breeding has been done between the assorted squash/pumpkin species.

Pumpkins are just a color and shape of squash. Most are in C. pepo, with most summer squash. It seems Acorn squash is also in C. pepo. So is Vegetable Spaghetti. Those should all cross with most pumpkins. But some pumpkins are in other species, with Butternut or such winter squash. The 4 species of squash do cross some, so you still have a chance of success no matter what squash you are trying with what pumpkin. But some are easy and some haven't worked yet.
Try it and see what happens.
Walter