Cardassians and Denobulans - agreed, they should be considered as Fed races.
Romulans, totally not. They get their own faction.
Cardassians will eventually have their own faction so for the same reason Romulans should not be Fed races neither should Cardassians. They added Klingons to the c-store for Fed playable species. That was mainly because of Worf being cannon. I am not familiar with any Cardassians or Romulans who were apart of the Federation so I canít see those being playable Federation species unless you use make an alien.