I am looking into this topic recently. It appears that some editions of the CECP protocol advise reporting mate scores as 10000-distance to mate, while at some point this was changed to 100000-distance to mate. I notice though in the engine-intf.html bundled with Winboard 4.8.0, there is no mention of mate scores at all in the section on "Thinking Output." So it is not completely clear to me what the standard is.
cutechess apparently supports both mate score options, via this patch:
https://github.com/cutechess/cutechess/commit/234fddf113ae0e9b491d348f93fb703089bf2258.
I notice though that in Winboard (I have tried 4.8.0 and 4.9.1), reporting either 10000 based scores or 100000 based scores does not seem to trigger any special behavior in the UI: in other words, the score is just reported as the engine sends it, and not as "+Mate10" or something similar.
--Jon