i wouldn't go as far as to say its cheating.
i think you would tho. only because your asking. what would u do if you were playing b2b, the other person played that tune at +4 then its ur go, would u go oh hang on, let me slow it down to 0 so i can beatmatch. if i saw u do that id move u out of the way and assume u cant mix.
honestly and i cant stress this enough. practice!
try not to rely on these sort of things. beatmatching really isn't that tough, just practice and you'll soon be able to do it in seconds by moving the pitch up and down 3 or 4 times.
too fast - too slow - still too fast - still a bit slow - moving it less distance apart each time. start dramatically, like minus 4 to plus 4 then minus 3 to plus 3 etc.. then when its in time its just minor movements to get it spot on. much quicker than writing the bpm on ur tracks or remebering them or any other bollocks like that.
the method u mentioned above wont work perfectly. especially if your 0 pitch locks in place. i'd be very suprised if they stayed locked for the whole mix without you needing to adjust the pitch or give it a little nudge.