I don't think you see any foreign flagged simple OSVs carrying cargo in the GoM. Those foreign vessels that are there are highly specialized and do work that requires capabilities not available locally.
There isn't a market in the GoM alone for large SSCVs, like Hermod, Balder, Thialf, S-7000 or the like and nobody can afford to build anything like that at a US yard, even for the worldwide market, much less if limited to a relatively small US market.
The same applies for the high-end CSVs, which is far more capable than the MPSVs that has been touted here as "equally capable".
If any such vessels should be built to meet Jones Act requirement they would have to compete on the international market to be economically feasible. It would only add to the already crowded market and keep the charter rates low.
This already applies to the existing vessels with such capabilities that is US owned, like the HOS and McDermott CSVs, all of which are foreign flagged. I don't know if any of them have US Mariners on board.
Forcing the Construction Contractors to carry heavy equipment from the yards to the CSVs in the field on Jones Act vessels only add to the cost and the risk, but does not add a "yuge" amount of jobs for US Mariners. If the CSVs were US flagged and manned, it would.
Besides, how do you carry and transfer miles long coiled pipes, cables or jumpers on reels weighing in at several thousand tonnes? If forced to they may then set up spooling bases in neighbouring countries to bypass the "ban".
As to crew cost on these same CSVs; I don't think you find that the Officers are costing any less than their US counterparts, when you add in even time, travel expenses, social costs etc.
The Iban Riggers and Pinoy ABs does, but they have years of experience from SSCV and CSVs. (Besides, they do not complain about everything, or sue for the smallest matter)
Whether you like it or not, the market for such vessels and personnel is International. To compete you have to have the "tools", the knowledge and experience. Without it you can only play on home ground. Even then, only if the market is willing to pay, or by protectionist means.
Right now it is possible to get hold of a fleet of vessels of very high standard at a very low cost. Some take advantage of that, in preparation for the upturn. Just look at Rokke, Fredriksen and Siam, they are all out there getting ready. Where are the Americans?? (Aside from ECO, Seacore and some Wall Street speculators??)