I was working with UE4 for a couple of days on a Surface Pro 4 i7 as well as on a Surface Book. The Surface Book was a pre release version so I had some troubles but the performance is great on both machines. Of course you can’t run huge projects with thousands of assets, but the overall performance is good enough to run the editor smoothly and to do some basic work. I don’t know why people are having editor problems on a Surface Pro 4 i5, because the editor itself was already running smooth on my old Surface Pro 1.
However, if you want to create a game with smaller scenes and less demanding graphics (as ZacD said) you should be totaly fine. If you want anything more, you need a bigger laptop. But isn’t there another reason for you to buy a surface? It’s not a common decision to buy a tablet for game development.