While that is a great cert to have for working any offshore job, is there any dive liveboard that actually requires it?
I think there was a thread by one of the flower garden boat captains asking that.... I don't think there were any 'yes' answers.
STCW 95 is not required on vessels of 200 gross tons or less that are 'domestic voyages'. (voyages that begin and end in the US).
It still is a good feather to have your hat/resume when applying for a liveboard job.
now working an offshore commercial ship crew, I think most require STCW 95
EDIT: Looking at the Agressor and Peter Hughes page, they require STCW95 for employees