No, TNG-era Romulans all had the ridges (plus an even more pronounced yellow/greenish complexion) which I can only assume was added to make them more visually distinguish them from Vulcans (as if all the giant shoulder pads weren't enough!)
I actually really liked the passing comment in Picard that noted the ridges are a trait of Romulan "Northerners," especially the fact that it was delivered as just a passing comment instead of a lecturing infodump. (It was one of the very few things I did like about that show.)
I assume the ridges would be a genetic trait that is shared between Romulans and Vulcans, although it could easily have been a specific ethnic trait of a segment of the ancient Vulcans, and the ethnic group that carried the trait all/mostly left Vulcan as part of "Those Who March Beneath the Raptor's Wings." It would make sense that acceptance or rejection of Surak's philosophy would follow along ethnic cultural lines with some cultures more willing than others to embrace it, and if the ridged ethnicity rejected Surak's philosophy for cultural reasons and were part of "Those Who March Beneath the Raptor's Wings" they mostly took the trait of brow ridges with them when they left, and they apparently mostly settled on the northern portion of Romulus (Perhaps Surak was a member of an ethnic group that the ridged ethnic group was especially antagonistic towards, and so they either rejected his philosophy out of hand or saw it as some kind of trick to weaken them? That certainly sounds like how modern Romulans think. It makes one wonder how close modern Romulans are to the ancient warlike Vulcans?)
I would assume that ridges still pop up every so often in native-born Vulcans.
The differences between Vulcans and Romulans would be cultural and ethnic, as the two populations didn't diverge long enough ago to speciate into biologically distinct lineages. They would be distinct populations forming their own ethnic groups with superficial markers, but should still be considered biologically the same species, and should be able to interbreed without any problem.* (As evidenced by Saavik.) It takes a long time for different populations to diverge into distinct species, especially considering the length of Vulcan lifespans/generations; despite it not being clear exactly how long ago (before the 23rd/24th Centuries) the ancient Romulans left Vulcan, not nearly enough time has passed for Vulcans and Romulans to have become different species.
*There is at least one novel that mentions that Sarek and Amanda needed medical/genetic assistance to conceive Spock, since they were completely different species.
