I was wondering the same thing. We go out next week for the appointee tour and was thinking about going into the branch office to open up an account. Maybe with the appointee letter they will?
With the appointee letter the USAA financial center (branch) should be able to open the account. There are branches in Colo Springs, Annapolis, Highland Falls.
USAA is closing many of its financial centers (branches) this spring, emphasizing digital platforms. The three above will stay open.
Check here for a location, and don't delay
https://www.usaa.com/inet/pages/usaa_financial_center?akredirect=true
I don't think it can be done online, since the SSN cannot be verified as a military member yet. Hard to set up a log-in without that critical first step.
I am awaiting feedback on the specific USAA number to call. They can usually get creative and take a scanned or photo version of the appointee letter. I hope to have that number this week. My USAA contact, a USMA grad, understands it all.