In a word: yes. The 550 (citation II, citation bravo) is a multi-pilot aeroplane so your hours will count as multi-crew time.
However this is not necessarily the case on the 551, which is the single-pilot variant of the 550, or the CJ's (C525, C526) which are single-pilot aircraft. On these types multi-crew time can only be logged if they are operated multi-crew under an AOC. In Europe at least, not sure how the FAA handles these things.
Hope that helps.