Would AC voltage damage the capacitor if using a low voltage rating capacitor?
I would pick something with more voltage margin, but in a theoretical sense this will work just fine, it is the voltage across the cap that matters, not the voltage between the cap and some external point. 

Actually in practise it would probably be fine as well, an electrolytic with a standing DC bias from a highish impedance source is a very robust sort of thing, but you never like to see 6.3V parts in a 6V circuit, just on principle. 

Regards, Dan.