Yes they certainly can if they want too.
If a male bison and a female buffalo got with each other and wanted to mate then they could breed and then you would have half a buffalo and half a bison as the baby.
I have never heard of any buffalo or bison breeding together but I'm sure it has happened many years ago even before humans existed.
Bison have existed for thousands of years so it is possible that a bison and buffalo mated before and we were not around to know about it.
But if you did have a bison and a buffalo in the same pasture and one was male and the other was female and they decided to mate up and have sex then yes they could mate.