I've seen the exact thing here in Durham, two of these fluffy white Spilosoma, one on each side of a leaf. I presume they had, or were about to, mate. I'm still not sure on the species either--they looked very similar to yours--almost pure white.

Mating does seem real plausible. The one on this side of the leaf has feathery antennae, a male. The one behind has much more thread-like antennae--surely a female. Sometimes circumstantial evidence is very convincing.

Patrick Coin
Durham, North Carolina