... or you could not do any of those things
and simply output status messages to sdout
What you could do, and would have a chance to be accepted, is to create a communicate-with-frontend protocol through stdin/out activated with a command line option. Then you'd change the code to encode the rom check/loading/etc information so that the frontend can easily parse and display it in whichever way it wants.
If you're funky you can even try to pass the window handle from the frontend to mame through that protocol (os-dependent obviously, would work under linux, dunno windows or osx) to avoid window transitions.
But you'll have to do it cleanly if you want to have a chance to have it accepted, obviously.