Personally I think that might be pushing the limits for such a small tank. I guess it would depend in filtration, how heavily planted the tank is, and the parameters of the water, such as gh and kh etc. The good thing about rummy nose tetra is that when the water quality isn't up to par their color will let yo know.
Yeah, they are mostly mid swimmer, but like the raspboras, will go all over. Both are good schoolers. Since I believe they are a tetra still mostly wild caught, you might want to make sure you have softer water, at least at or below 7.4 and they won't breed unless it's more acidic and warm.