I haven't got GalCiv 2, but Frank Klepacki, the original Red alert composer is supposed to have done RA3 music (Hell March 3, at least [e digicons]:grin:[/e] ), but it's not uncommon for two different musics to have similar passages, for example, one game i played on SNES had music that had exactly the same part as a TV-series tune. The shows in question was made by finnish for finnish, so i doubt the american composer had heard that.
BTW, there are indeed sound banks, that can be used in any game, TV-series or movie, but in my understanding they are only sound effects, i can't count how many times i've heard the exactly same "rusty door opening" sound, or the exactly same dog whine, or the exactly same angry cat, or...