I doubt you will be able to use OA at all in your scenario. The
EVO II also needs a lot of light to take a decent image; I've found F2.8, 1/20s shutter, and ISO800 is the optimal low light settings. I don't know how bright your lights are or how much you will be able to light the cave but I am imagining a noisy underexposed mess.
I shot some caves in Va a few yrs back with a DSLR and I wasn't able to get good exposure without using F2.8, 5s shutter, and ISO3200 and that was with a full frame camera and plenty of lighting. If I were you, I'd do some above ground testing at night with the EVO and your lighting setup to see if it is even feasible from an exposure standpoint.
I think you may find a traditional camera with a tripod and a long exposure will work better.