In the grand scheme of things it was correct to keep them "invisible" to Starfleet, for obvious canon reasons and because the Romulans had an interest in not letting their connection to Vulcan be known to Starfleet and especially the Andorians.
There are about 2.000 years between the exodus of the Romulans and their encounter with the budding coalition at the time of Babel One. With their longevity that's too few generations for any major genetic differences to occur (the ridges are already a stretch). That means, any weapon or chemical or biological agent that's effective against Vulcans is also effective against Rommies - and the Andorians must have developed plenty of those. So they have a vested interest in keeping their ancestry hidden.
"Are you planning to excavate this rectangular area?"
"Yep, I'm diggin' a hole, T'Pol"