If you can grow ficus indoors then you can also grow root over rock ficus indoors.
ROR is all about balance. The tree size should suit the size of the rock. Big tree on tiny rock just would not look good to me though sometimes a larger tree with roots over a very low stone can look good.
Pick the rock to suit the anticipated size you want to grow the tree which often depends on leaf size. Steer clear of real big rocks as they are simply too heavy to manage when it comes to turning the tree for even light, repotting, etc.
Root rot is the result of way too much water rather than the size or style of bonsai. If you manage watering properly there should be no problem.
Figs naturally grow aerial roots so no need to grow out long roots in pipes, etc. I still prefer foil to get roots growing real close to the rock looking natural but ficus don't have the same urges to throw new roots laterally so they can simply have the roots draped over the rock and planted in a pot with reasonable certainty the roots will still be where you placed them a year later. Whatever establishment method you feel comfortable with should work with ficus. So much will depend on what conditions you can manage while the roots get going.
F. pumila do not seem to develop thick roots down here so I'd avoid it for real ROR but they might make good root on rock trees.
F virens should do ROR extremely well. They are known here as 'strangler' figs as they tend to germinate up in trees then the roots grow down to the soil below.
I am not familiar with the other species you have but if they grow roots they can be used as ror.
One of the best ficus rock plantings I have seen is 3 F. rubiginosas planted on a large vertical rock - see pic below. That's around 1m tall but the 'rock' is made from cement sheet and construction adhesive so not as heavy as natural rock. The roots do not need to be long enough to reach the pot initially. Plant the trees in pockets of soil and provide plenty of water and humidity and the roots will creep down the rock and reach soil eventually. There's no way root rot would be a problem for a planting with roots exposed like that.
One word of warning. Don't start with too many roots. Ficus roots thicken and spread quickly. My earliest attempt completely swallowed the rock it was on which left me with root over instead of the anticipated root over rock.
