Emulator Cheats

What's the native character set for cheat.dat? For example, if I input all my cheats in a specific character set (eg. Shift-JIS or UTF-8), would they still work?

And if cheat.dat is Unicode-compliant, is the byte-order mark required?

MAME itself doesn't support any character formats other than ASCII as implemented by DOS. The cheat engine doesn't implement anything beyond that.