I recently figured this out and thought I would post it in case others are struggling with this. MAMEoX is a build of MAME which runs on the Original Xbox Console. I use it to play classic games on my TV, and for years I thought it did not support Cheats for infinite lives, etc. Turns out this is not correct. In order to enable Cheats you should do the following:
Get the latest cheat.dat file. Make sure it is in cheat.dat format, the last version supporting this format was MAME 1.26.
Now FTP this file to your MAMEoX directory, in the /general/ subdirectory.
Now, after launching a game in MAMEoX, press BACK + WHITE on your Xbox Controller to open MAMEoX's in game menu, and select the Cheat submenu.
And then Enable the relevent cheats for the game you are playing:
Enjoy infinite lives on your favorite classic aracde games!
