1. I think GI confirmed a military base to be in the game.
2. Hydra confirmed in the game.
3. Trailer 2: Trevor jumping out of what appears to be an Army cargo plane via an Army looking Jeep-like vehicle (with the star on the back).
I'd say at this point it's highly likely there will be tanks. I definitely would want the Rhino. Something about crushing a car using the RAGE engine seems so satisfying. They should make them hard to get though, not just walking into a military base and taking it or through a cheat code. There should be lots of opposition like there would be in real life.
Like getting a 6 star in III burning the occupants and the. Going about getting the wanted level reduced icons --- Cheaters always deny its cheating