All of this talk of wages. It really depends on where the vessel sails, what kind of vessel it is, and a number of other factors.
A vessel sailing seaward of the boundary line must pay their deckhands $614 a month as of January 2016. It did not change for 2017 or 2018. If the vessel stays shoreward of the boundary line, they are required to follow the state minimum wage law. That's a 30 day working salary. So as long as the seaman is making $20 a day, all is good.
You are correct about the subcontract law, the tests for being a contractor fall in place here. Most crewmembers don't meet the requirements, as they have certain training they must have. In our case, as long as the crewmember was not in a safety sensitive position (gas blender, chef, steward) they could be subcontractors. If they required training (Captains, mates, deckhands) they were employees. If the vessel ever charters to any branch of the federal government, they must meet certain salary minimums. A Ordinary Seaman is $114 a day, Able Seaman is $154 a day in Monroe County FL.
All crew are Jones Act qualified, which means they are covered by your Workman's Comp (or Jones Act) policy while working on your vessel in crew status. Crew status means "In service to the vessel". We had to be very careful when we ran tech trips, as we had mates (who tied in the shot line), gas blenders (who filled cylinders) The DSO (who reviewed but did not dictate dive plans) and the regular crew. Those folks were there for tips and diving, and we never asked them for more then their jobs, as to do so would have placed them in service to the vessel and therefore would have qualified them as Jones Act crew, which costs me about $1,000 a head for insurance.