It is probably possible. Some women claim to have gotten pregnant from cum on a toilet seat. A lot of women won't sit on the seat. theoretically a woman could get pregnant if a guy cums on her leg or belly. But it is really unlikely. Sperm are really pretty fragile. To be able to live in a cunt, they need the chemical protection of cum and precum. An asshole is a pretty harsh place to live and the sperms only know where to go by smelling the cervix mucus, which is in the next hole over. So to be able to know where to go, sperm needs to smell the cervix. That is asking a lot for something out of the cunt.

There is at least one woman who got pregnant without fucking the guy, if that is to be believed.