I would assume based on judgements in other copyright cases, that as long as you broke no encryption, you own the ROM legally, and you did not attempt to profit or commercially gain, you would be OK. US law, before the DMCA protected fair use, but was severely limited by the DMCA. If the original producer did not take steps to limit your use, you were basically free to use it as you want, for non-commercial uses. I would say that if you were not profiting from it, you would be OK.
I am not a lawyer, but am very interested in copyright law and fair use. Take my comments as such.