"Can"?
JWs "can" do a lot of things. But there are many things that will result in varying degrees of ostracism.
Dating an unbeliever (in JW-world, an "unbeliever" is someone not baptized as a JW) is pretty high up on the bad list.
A JW wouldn't necessarily face "official" sanction (unless naughty bits are rubbed together) but any JW "dating and courting" an unbeliever would face an increasingly difficult set of "unofficial" punishments from the JW community, designed to encourage him/her to break it off.