There aren't any Cave games on PGM cart-based hardware (unless you count Bee Storm, but that was made by IGS). Cave PGM games existing on cart are sort-of-hacks anyway from the single-PCB hardware.Wouldn't you have a problem with them too if you do a PGM multi?
90% of people that want a PGM multi probably want it only for the CAVE games...
If you're making a cart-based PGM multi and not selling the games, Cave doesn't really fit anywhere in the equation at all.