I've used QS between layers of UPP because my car wasn't dirty enough to wash. Seemed to work just fine.
BTW, QS has worked great with every sealant and carnuba LSP I've got, and currently that is:
#16, NXT, Glanz Wax, Pink Wax, Shokar Sealant, Carnauba Moose, Souveran, Paste Glaz, S100, Race Glaze Polish/Sealant, Z2 Pro, Optimum Car Wax, UPP, Stuf Carnauba and Wolfgang.