USAA is always striving to keep up with technology and member needs. In a Facebook post from December, official USAA representatives responded to this question with "We are looking at several mobile wallet options and will adopt functionality that can reach and benefit the most members. Thanks for the question. - Mike"
We, here in the forums, are not banking experts. You might try to contact a member services representative for an answer on the progress of this program via email on our contact us page or via phone at 210-531-USAA (8722).
Still, because of the nature of your question it may just be something we have to wait out to see what the latest news will be.
I have never used isis, but I do use google wallet and have my USAA credit card linked to it. When I make a purchase with my google wallet mobile tap and pay app it is charged to my USAA card. Does isis work in a different way?