Hi there, and welcome to the forums. Unfortunately, the Register Product thing on Impulse only works globally with Stardock products to my knowledge. You may be able to Detect the application using the Impulse client to get it added to your list of applications there, but that wouldn't provide application updates through Impulse or anything of that sort, to my knowledge.
If you're unsure, I would try getting Impulse to recognize the demo of AI War to see if it will work from that angle -- as far as Impulse as concerned, there is no difference between and unregistered and registered third-party copy of AI War or TZR. So if you can get it added in a way that is satisfactory to you, then you can go ahead and buy it with confidence wherever you want. If not, then having a registration key from somewhere else won't make any difference as far as Impulse is concerned.
Wish I had better news.
I'll get up with the Stardock folks and ask them what's available at this stage with Impulse (with Steam, they had to literally import all our keys to make the Steam Key registration possible), and I'll post here with whatever news. Might be a few days before I hear back, though, as it's a busy time of year at most development shops.