While it is possible to have a Delta configuration with a "Elevator", this is not a true delta configuration and usually with this type of setup, pitch authority is much less authoritive than what elevon control would provide.
I am no aerodynamics expert by any means but.... Setting the roo up with seperate (outboard) elevators/ailerons is inducing instability into a fairly stable platform. If you had a control surface at the center of the delta for pitch control you might get good response but I would not attempt using the wing surfaces as seperate controls. And for that matter, why would you want too?
BTW.....almost 300 flights on my roo with single 8411's per elevon without a hitch. The million dollar question........ Can you actually land a roo with one failed elevon servo ( when using 4 servo setup) ??
Todd