There are at least two things in every employment case, and at least one additional thing in the company principal case, that will keep wages anchored to dollars no matter what form of unicorn dollar we come up with next:
* There is a dollar-denominated minimum wage
* There is dollar-denominated payroll tax and, for contractors, dollar-denominated self-employment tax that scales in dollar-denominated amounts whether you're paid in moon cakes or rare freshwater fish.
* And, if you're a company principal of a non-passthrough entity, there is an IRS requirement that you be paid a wage that corresponds to the fair market value of your role, and anything you do to not pay yourself a reasonable-looking dollar-denominated wage stands a good chance of getting you audited (this rule being one of the primary ways business owners attempt to avoid paying taxes).
It's only been fairly recently that the Department of Labor has issued opinions about foreign nationals being paid in foreign currency based on the current exchange rate available in the vicinity of the employer; that is, there are very specific cases in which you can pay someone both Euros and Dollars. Making geeky assumptions that, because some PHP program somewhere generates some number people call an "exchange rate" that means Bitcoins get you around the FLSA minimum wage... dubious and risky.
(Might you be conflating payment in bitcoins with payment off the books?)