I can confirm from very recent experience (LHR-DME-DOH) that air-side transit without a transit visa is very much possible at DME also. Can't speak to the ability to have someone retrieve/check-in bags (as I was travelling HBO), or to the ability to have your boarding pass printed (I had a printed QR boarding pass with me) but there certainly was a transit "check-in" desk staffed by a single person even in the middle of the night. The transit security check did involve a couple questions to confirm I was in direct transit from, but otherwise was pain-free.
BA check-in at LHR were more paranoid than the folks at DME were - two phone calls were needed to confirm I was ok to be checked-in without a Russian visa, and one more verification from a supervisor at the gate before I was allowed to board. Having my printed onward QR boarding passes helped tremendously there, so would strongly recommend having those handy when checking in for your positioning flight.