I was wondering the same thing about the pull-pull on the DP ultimate a few weeks ago. I first flew it a few times with the pull-pull setup on the elevator. It worked ok, but they would both not center the same. I was also worried about flutter. Last week I put 1 elevator per each half in the tail at the bottom of the stab and just run a pushrod back there. It works a lot better and flies better. I have more torque now, and it balances out better. I use a YS 140. The rudder is fine and works great with pull-pull.
Ryan