I just tried to claim the T5/T6 ships for my KDF aligned Romulan Republic character (who's a Reman, but I wouldn't expect that to make a difference).
I'm unable to claim the following ships that I own through the Aquire Starships interface
Varanus Fleet Support Vessel
Marauder Flight Deck Cruiser
Kor Bird of Prey
Qa'Tel Flight Deck Raptor
I am able to claim them through the C-Store though.
Could this be the way that the ships are categorized? So Romulans don't get to see Raptors for example?