That should not be a problem however I have not tested this. When using the guest identity sequence in ISE you have the ability to add the databse you want to ISE to check. I do not see why you could not add another radius database to that selection. Here is a thread on configuring this -
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...