Yeah, selling the games would muddy the waters a bunch. With freeware at least you have the excuse that, well, it's free, and it's a 30-something year old system.
Roland may be proactive about their ROMs, but until Sierra or whoever holds the rights at this time start making requests I'd just stick with freeware distribution.
(Besides, you don't need MT32 ROMs to play. Whatcha gonna do, include a copy of Munt? A shortcut to an eBay search for real MT32? I'd say just offer General MIDI and keep the MT32 as a bonus for whoever already has the ability to play that.)