I feel like Hitler would channel his anger, and would be all fists and elbows. Trump definitely has the size advantage, and I imagine him keeping his head back to guard his hair, while taking big swipes at Hitler like King Kong swatting at fighter planes.
I think it comes down to whether Hitler's rage blinds him, and he lets Trump get ahold of him. I think in a bear hug, there's not much Hitler can do, especially when Trump just kind of leans over and takes them both to the ground. After that, Trump rolls on top and suffocates Hitler.
If Hitler can keep his cool enough that he doesn't do something stupid, I think he can come out on top. He seems pretty springy and scrappy from the footage I've seen on the History Channel. I think it's duck, jab, dodge, and elbow. If he's lucid enough to get his feet involved, he can take out Trump's knees, which are clearly a structural weak point, given Trump's build.
Honestly, I really think it could go either way. I like to imagine that Steve Bannon gets thrown into the pit with them, has to make the painful decision of who he's going to help.