Fyi, med school is very much unlike college in the way textbooks are handled. To say that a med school "uses" a textbook really doesn't mean much. We certainly have lists of recommended books for each subject at the beginning of the semester, but professors often recommend multiple books for each field and it's up to you to determine whether you want a book at all/ which of those you like best. And still, if you want to use entirely different books that's totally up to you.
Each subject is also different: owning a number of different anatomy atlases for example is somewhat useful because you can see different depictions of the same thing, but it's mostly a waste of money (most people use Netter and may have another one to compare and contrast). Histo is best when you have a lot of examples, so people are more likely to have multiple books depicting the same stuff.
So yeah, a number of us own Wheater's. A number of us also own totally different histo textbooks, but having Wheater's around might be handy if we just want more examples of images. If you're short some cash, then sell it, otherwise I don't see why you shouldn't keep it. It'll make for a good reference.