Some very interesting thoughts on the Remans ... I like the idea of them simply being a conquered race.
Agreed, would explain why the Romulans treat them as a mix of slaves and cannon fodder, and that it was such a surprise to the Federation that a Reman could become Praetor.
The graphic in Nemesis sowing the Romulan system unfortunately does not make much sense. In general, the closer an orbiting body is to its parent, the more likely it is to be tidally locked, for example our own moon. It would appear that Remus is further from its sun than Romulus, so Romulus should be the one tidally locked.
Given that Remus looks totally barren (unless this is to do with excessive atmospheric pollution after being used for heavy industry) and that both Romulans, Remans and Shinzon were able to breathe the atmosphere in the mines, it would make sense that the Remans evolved on a standard CLass M planet and were exiled there by the Romulans, probably from Romulus itself. It looks unlikey that advanced life would evolve on Remus.