Hey Ronald,
I know that this has been fixed in the 7.x version of code for NAC. New deployments on 7.0 will have SHA256 certificates for captive portal, RADIUS, and Internal Communications. Not sure, if this has been fixed for wireless but NAC should be unaffected by SHA1 deprecation.
If you installed NAC when it was issuing SHA1 certificates they can be easily regenerated.
Thanks
-Ryan