Hmm, could be ultra magnus, could be just a truck they use to carry characters, like in ROTF they used a truck that carried the three bikes didn't they? or maybe it was troops on quad bikes? i don't think we should get our hopes up until we get solid evidence or confirmation!
On a sidenote, has anyone seen jolt on location? i hope they dont exclude him from the film, with all these characters that they won't be bringing back i hope they have explanations for it rather then just not mention them (chromia, jolt?, wheelie, skids/mudflap) i know we saw pictures of what's believed to be new alt modes for the twins and nothing else since so they might be in a scene or two and thats it, but i can see them not even being mentioned, would be simple, could say that NEST sent all them on a mission elsewhere, or that the main autobots in this one have been specially selected for the missions in hand, or just simply say they all went back to help on cybertron! That's the main problem i have with these michael bay films, the plot holes and when characters simply dissapear never to be seen again (i'm looking at you barricade and wheelie) but i'm happy as long as there's big robot fights