I have kept both neon dwarf rainbows (praecox) and threadfin rainbows in a 10 gallon before. But I only had a few of each. there is not room for a nice school in a 10
but as mentioned, most other rainbows are not a good fit.
IMHO, 10 gallons is way too small for neon rainbows as well, threadfins maybe, but only if it's a species only tank, because they should be in a school as well, and their fins are too tempting to most other fish, especially in such a small space.
All rainbowfish (maybe with the exception of threadfins) need plenty of swimming space. In general, I would not keep rainbowfish in anything smaller than a 45 or 55 gallon since they are so active and most get up to 4 inches long and are schooling fish.