Does this make sense?
I cannot have the nrf24's go through the air,
Why not that is what it is designed to do.
it must be through the guitar cable. (will have no interference if I turn and am between the two nrf24s,
If you want it to go through a cable then you have the wrong device your transmitter will not work like this at all. You need a modulation device some what like that used for communications through the mains.
not having a 4 inch antenna sticking out of my guitar
Why, that picture you posted showed it had a PCB antenna, why do ypu want another one?
So, my main question: will a very very low voltage AC signal hurt the nrf24s?
Yes it will.
I would assume not, since it is well below its operating voltage (even if its AC).
There are more ways of damaging an input than taking it over the supply voltage. A 1V signal is massive compared to the signal it is designed to amplify, it would not surprise me if it blew the front end.