Ok, so I set everything up, probably I can't get better with current setup.
I used stereo.lua setup in DCS to render stereo pair, and I used free tool - Oculus Overlay to make screen wrap (NThusim didn't work for me in DCS)
Eye separation in stereo.lua 0.6 (-0.3 and +0.3 for left and right views), 0-for convergence (you shouldn't use any convergence when render for Rift, otherwise images will not match). And tweaked Oculus Overlay to get image of a right size and so on.
I used TrackIR5 for tracking, and HOTAS + rudder pedals for flying.
First I was very happy that everything works now and I don't have nausea from this setup, and everything is in proper stereo. BUT damn the whole experience is crippled because of super low resolution of current DevKit and bad screen in general - color reproduction, pixel smearing... I mean it is awful, you can't read any gauge in Ka-50 or Su-27, you need to zoom in so the gauge occupy huge portion of your vision to read it. And I'm not telling about looking for ground targets.
I did some ground attack mission on Ka-50, and even killed some targets, but as it is now Rift DevKit 1 is useless for DCS. Sure one can experiment but certainly not playable. So now I'm waiting for hi-rez Rift to repeat my investigation on VR DCS. Shouldn't be long now? ;)