In Scientific Mandate, the Romulan and Federation will be working together in a joint scientific endeavor between the two peoples. The Romulan crew will still be aligned with the Romulan Star Empire and below are a list of equivalent Romulan ranks, based of canon sources and Star Trek Online.
Cadet = Uhlan
Ensign = Sublieutenant
Lieutenant = Same
Lt. Cmdr = Centurion
Cmdr = Subcommander
Captain = Commander
Admiral = Same
General = Same
These Romulan and Federation ranks are available here (courtesy of the magnificent Martin Thompson): http://www.mediafire.com/download/p2nz1b8aqlgtb11/zzzzzrpgx_default_rom.pk3
Hey SFC, I could make a rankset for you if you don't know how to do it (Its basiclaly an expansion on the existing rankset). Just drop me a pm if you would like that.