Dollar-cost averaging works the same way with any type of investments. Not just Bitcoin. It means that you are investing a fixed amount of money (dollars) at regular intervals.
And what if what you’re investing or the amount of money you’re investing isn’t in dollars but either another fiat currency or in the case of bitcoin or something that totally have nothing to do with Dollars.
The OP has asked a very thoughtful question. Would you still call it DCA in this case?