RIS is a non cannon term for Romulan Imperial Ship. To my knowledge it has never been used in an episode of Trek. It only appears in computer games. IKV is cannon, as it was used in several episodes... Trials and Tribulations, and Emmisary (TNG) are the two that come to mind first.
Romulans always call their ships Warbirds...If Warbird was used to just describe the D'Deridex, then Commander Donatra would have used a different term when she announced herself to Picard and the Enterprise in Nemesis. Also I seem to remember one TNG episode where they encountered a Romulan Bird of Prey (Ala Kirk's time) and it was also called a Warbird.
Perhaps it should be reiterated, ONLY what is shown on TV, or Movies, are cannon, use that as a generalization when you have a question. I believe that there are only two novels, both written by Jeri Taylor, (former producer of Voyager) that are considered cannon as well. No Games, no Magazines, (although Star Trek: The Magazine was officially licensed by Paramount, and only did articles based on what was shown on screen, (or in some cases left on the editing floor for movies) so you could consider that a source, maybe), and definately NO TECH MANUALS. (yes thats a jab at Star Wars v. Star Trek in Five Minutes because the exact same thing applies to Star Wars and most other Science-Fiction programs out there)