A. In general, proving draws (from fortresses) is easier than proving wins for humans. I guess you could write K+Q and K+R as induction proofs, and in general (see B+N) you want to progress from one goal to the next, but clarifying this is in an explicitly mathematical way is not typical.

As for actual publications, chess is not so apparent, but the B+N ending in Kriegspiel was proven to be a win by Ferguson, notably published in a TCS (theoretical computer science) journal.

http://www.sciencedirect.com/science/article/pii/030439759290344F

He later handled B+B but I think it remained unpublished.

http://www.math.ucla.edu/~tom/papers/unpublished/kriegbishop.pdf

Maybe Timman's famous R vs B and a-pawns analysis could be considered similarly weighty as a publication (the old-school analyses of Cheron and Averbakh largely before computers are of course error-prone, but did make some attempt to mathematize the process).

B. There is a lot of misunderstanding regarding computers and fortresses, as usually the humans do not use the right tools (they will use a general computer program and "root search" for instance). Moreover, phrases like "decisive advantage" are not really meaningful to a computer until a win is actually proven (for instance, today's game of Giri versus Hou Yifan had some interpretations of computer scores erroneously giving a "decisive advantage in a 7-piece rook ending at a point when it was theoretically drawn). It is diverging into peculiarities of chess analysis, but one simple yet often superior alternative (indicating the above Mamedyarov-Caruana draw quite easily, though proof is a different question) involves seeing whether the computer's score increases or not as the search goes on (e.g., is some progress being made, such as pushing a pawn?). Of course, that will not likely help in extreme (contrived) examples, but in most practical cases this suffices. The programmer of "Houdini" had a special mode (reduction of 50-move rule) to try to suss out fortresses, demanding progress to be made faster. There is also Bleicher's "Freezer" that is a human/computer interactive proof: you make the "rules", and it iterates over positions.

http://www.minet.uni-jena.de/preprints/bleicher_04/FREEZER_.PDF

http://www.freezerchess.com/