I now have a SDFCU account setup and working, but it wasn't quite as easy as I'd like, so I thought I'd share my notes.
First, you have to have an ACA account, which costs $70. Their credit card wouldn't work for me (using various cards/browsers/operating systems), and I had to email them, then send the money via PayPal.
Once the ACA was set up, creating the SDFCU account with id verification was easy enough. Transfering money from Vanguard via ACH was easy, and Vanguard supported direct authentication rather than microtransfers.
Enabling ACH from SDFCU required several email exchanges before they enabled a menu option for "External Transfer". In theory, there should have been a menu option in the "Online Tools" box for "External Transfer Access Request", but I didn't have that.
Setting up Wise in SDFCU was micropayments, and there was a day's delay before the menu option appeared on the CU web site to enter the transfered amounts.
EDIT: I've found that SDFCU limits ACH payments to $3,000/day and $6,000 per 28 days. Amounts over that would need to be via wire transfer, where you fill in a form and submit it for approval.
https://www.americansabroad.org/sdfcu_faqsHopefully this will help others.