You're best asking the adsense support team. I'd say, from a google point of view, it's a grey area if the roms were once copyrighted. (I'm wondering if it's "abandonware".)
Public Domain roms are freeware roms created by everyday people like me or you for certain platforms, these are only owned by the person who created them like any freeware program and as long as you have their permission then the rom is legal, these aren't famous games roms but ones created by people themselves, hence why they aren't copyrighted and are free.
A rom site is a place you can download old console games (Like Nintendo, Sega etc) and play them on your pc, these are called 'roms'. Those are highly illegal, but public domain roms aren't famous roms or ones that were released on a platform but instead a freeware game created by a everyday joe who has given permission for people to use the game on there site.
Ah i see now .. Thanks ... (I was thinking of the drink - Rom). I guess, if the activity is legal, Adsense is allowed. You might wanna give them an email to have peace of mind.
It sounds like ROM in this case are programs that get burned to Read-Only Memory chips not to be confused with PROMs, EPROMs or in this forum, ECPM or CTR.