If the one game he really wants happens to be in the Windows 8/RT app store (he'd have to search for it first to see if it exists), then that would be compatible with the controller, or use the touchscreen. If it's not in the store, he can't play it on a Surface.
The Surface RT/2 line's biggest draw is the inclusion of MS Office. If he's not going to get decent use out of that, then the purchase would frankly be a waste. He can play games on other tablets, albeit not xbox. This was not meant as a pure consumption device. A Pro is also not a good choice as a "gaming first" device even though it can run Steam and plenty of other low-medium weight games; that's a productivity tool first (for gaming, one is better off building/buying a desktop anyway).
Ah, yes, CoD will only run on a Surface Pro. That's an expensive piece of kit for just a computer game, if that's really all he's interested in, unless he doesn't have a laptop or desktop and it would be his only computer.