Leaving aside how to apply marxian analysis to household relations, non-professional sexual partners, and so forth - the case of how people conceive cam sex workers using these things is an unambiguous example of marxian fetish. Your "human relations disguised as a relation between things" is laid pretty bare, there. That it also puns as "fetish" in a more conventional vulgar sense is just icing on that cake.

Ugggggggh I have a book chapter waiting to be published on ideas of labor and proxemics in digital intimacy that covers some of this.

So like, remember to check for that in September.