Finally found documentation on BMW's website of the loyalty credit here...
https://www.bmwusa.com/loyalty/x5.html
What's confusing is the page refers to the 2018 X5, but the picture on the page is of a 2019.
What is clear is that the loyalty credit applies when leased or financed. So, my conclusion is that one can qualify for the BMW loyalty + the USAA $250 credit, or the USAA $1000 credit, but not both.
Local dealer indicated the BMW loyalty credit is $1250, adding the $250 USAA when credit yielding a total of $1500. (The page I linked to above says $1500, but it also says 2018, so not sure.)
Dealer also indicated that minimum amount and term financed with BMW FS to receive the BMW loyalty credit is $7500/3 months.