Nope, UT2004 runs on the UE2 engine. (which is redundant because I'm saying Unreal Engine 2 engine lol ) We're talking about UT2007 (which recently got renamed to Unreal Tournament 3) which runs on the newer UE3 engine, and will be released this summer hopefully if it doesn't get delayed.
As for Tiberium fields, they'll be a mix between Renegade, C&C3, and the original Command & Conquer (Tiberian Dawn). They'll have C&C pods, with a Renegade-ish ground texture, and those vein things at the base of the pods like in Tiberium Wars.