Acoustic only venue

That's a very odd rule, why can't they have sound equipment like mics and speakers?

If the space is small and sort of "enclosed" (rather than a large open field) then it should be fine, but I'd ve worried the sound would disperse weird outdoors.

By "acoustic," do they mean that the vocals and instruments must be non-electric varieties, or do they mean no amplification systems? For musical instruments, there are still acoustic guitars with pickups and electric violins which require amplification.

I could probably appreciate the non-amplified sound as long as the instruments are not too far away -- or the musicians wander around from table to table.