to my knowledge, STCW 95, is not required for a typical (OUPV) 6 pack license in the States.
But if you're contemplating any work overseas, or the carribean, STCW 95 Basic Safety training will be a requirement. Or as Redstripe states, any yachts that will visit foreign ports would likely require you have it. There are 3 day classes for under 200 ton...and 5 day classes for 200 ton and above. The classes I see are in Mobile, Jacksonville and a few other locations.