Booked in I/J so listed as earning on the Delta chart.
Ticket shows on MU's Ticket Validation service and I was able to use their seat selection tool to pick some seats.
I guess only concern is getting into a situation where I need to submit the receipt from Priceline to Delta and Delta pulling the "no Priceline.com" bookings from their T&Cs. Probably over thinking it (and I know the PL.com clause is specific to the name your own price).
I have had no issues caused by going through priceline.com for MU purchases and claiming DL miles.
In this case you are using priceline as a vanilla OTA. The fare is a normal published fare from MU (though only offered through limited channels).
When I did have issues, they were always when I failed to insure I had my DL FF# on the MU ticket as I checked in. So verify that at check-in even if you previously verified on the web.
I was never asked for a receipt or BP from DL to fix this when I did have an issue. I submitted my ITN and they could verify I was on the flight,