There are DOT legal harnesses out there, essentially what make it DOT approved is the release mechanism (push button versus cam lock or latch).
Just make sure your set up allows for proper installation angles of all the belts with a hans and you should be just fine.
Ideally you want your helmet below whatever rollover protection you have. I cannot tell from the photo, but usually a race seat like that you end up with a lower seating position, and you could remove the foam padding in the seat to get even lower if you needed to.
My track/autox car has the recaro pole position seats, they are actually quite comfy & I like them a lot. I have them mounted on sliders still and that is enough adjustment for me, I don't miss having the recline option, the angle is about the same as my normal driving position. My bet is you'll leave them in more than the stockers
