I don't think I've ever heard it as anything other than screen cheating. Screen hopping sounds like you are switching from screen to screen or something, and screen-looking doesn't have the same easy/lazy to say flow of the consecutive ee sounds. As such, screen peeking/peeping would work, but sounds kind of silly I think. Not that it matters, if someone complains that someone else is "screen-somethinging" on split-screen, everyone will know what they mean.
Back in the day when splitscreen was actually common. me and my mates used to ***** at each other over screen cheating, but since it is pretty much impossible to not glance down/up when unexpected movement catches the corner of your eye we didn't honestly care. Unless someone was blatantly using it constantly, in which case they had to pass the controller on. It can be helpful sometimes though, it has been a lifesaver on occasions where there were two people left walking around a big map fruitlessly trying to find each other for like half a goddamn hour.