SC4 used Ubis version of UE2, which kicks much ass. I kind of thought they would use assasin's creed engine for SC5, but if it's scrapped who knows what is up.
I wanted rainbow on the graw engine so bad. That engine is also the ubi branded UE2 engine. It is barely anything left in it that is original unreal, but it is the one they used from splinter cell 1.
They really got hosed with UE3 for vegas, they had to take what they could from Epic (UE2.5) and make the game work.
SO yea, I was hoping they ported the engine, but i guess it would be too much work.