I'm thinking about this for my WASR. Everywhere I see T1s used on the EE and such other forums they are $500+ used which is over the cost of the MRO new so I figure why wouldn't I buy a brand new RDS for that price? I've also been looking for a good way to try one out anyways. I'm only wondering about cowitness on the Ultimak.

Well I can kinda answer your question. First off, Ultimak is good to go all the way. I have a PA micro clone on a riser on a Mak that has been flawless from day one. I see no reason why mounting an MRO would not work.
I cannot address the co-witness issue as that is of zero use or application for me. I don't like cluttered fields of view in my optics.
Try it out. At worst you have a mount and sight that needs a riser of some sort to work. In my case the riser I used allows me to see my irons simply by looking beneath the Micro clone. But, IT WORKS FOR ME. ymmv

I originally used a Primary Arms cheap model RDS ($80.00) and it worked great on the Ultimak. I switched to a low mount 1.5x handgun scope. I like the crosshairs better as far as accuracy is concerned. Eye relief is something like 14" and that works great as well.

I have never run the rifle really hot which has always been a concern to me. If high heat will effect either set-up I do not know.