There's several helicopters around but none jumped out at me as the same type as Skyhammer, but I'm not great at telling them apart.
It's definitely the Xantium that goes to the moon to pick up Sentinel Prime. It's called that by name as they approach.
As to that question of "9 Autobots" I see two possible answers. It's Simmons who says there are 9 Autobots, not any actual official at the base, any NEST member or any Autobot. Just because no one corrects him doesn't mean he was correct.
Simmons has come straight to the base from the hospital after the car chase. He doesn't know Ironhide has been killed (who would have or could have told him?). He doesn't know about the Wreckers (who have never left the base). So as far as he's concerned the 9 Autobots include Ironhide, Brains and Wheelie and not include the trio of engineers he's in the dark about.
The other possibility is that he's just looked at the camera feed of the convoy and counted the cars heading towards the ship (of which there's nine), and just referring to what he can see, and the little guys (which he must only see as pests) slipped his mind.
Next time I watch the movie I'd like to check the Autobot ranks in the final battle scenes. At the very end only Prime, Bumblebee, Ratchet and Sideswipe are present. Is it possible that Dino or the Wreckers may have been shown falling in battle too?