@Paul_H Are you sure on the "Cisco ISE is only NAC that can hand out SGTs"?
In a pure Cisco Catalyst environment this may be the case as you need Cisco ISE to no only act as the RADIUS authenticator, but also to authenticate the infrastructure and create the source SGT to destination SGT matrix that is then downloaded to the switches when requested.
In a pure Cisco Meraki environment I was under the impression that the infrastructure is authenticated by the Meraki cloud, and the source SGT to destination SGT matrix, i.e. the Adaptive Policy matrix, is also managed by the Meraki cloud. Using these alone you can statically assign a port to an Adaptive Policy Group. If you introduce 802.1x (for dynamic Adaptive Policy assignment) then my understanding is that all the RADIUS server needs to do is return the AV Pair to assign the SGT number. Now admittedly this is in the Cisco AV Pair format, but so long as the RADIUS server can return this pair in the required format then surely it can inform the switch which Adaptive Policy to use? Or have I missed something?
(Don't get me wrong, ISE is an awesome platform, but is it really needed for a simple Meraki network using dynamic Adaptive Policy?)