I don't use cheats myself, but it reportedly works when the exact same settings are made through QMC2 as you would on the command line
. That is, enable cheats and set the cheat path: -cheat -cheatpath <cheat-path>.
Please send me the settings you made here (or your qmc2.ini) and the command that's issued by QMC2 to launch the emulator (see front-end log). In case you use relative paths (i.e. default paths), it may just be that you forgot to specify the working directory
that's used when the emulator is launched.
So, best is to upload both files (qmc2.ini and qmc2-mame.log) and post the links here