Hi Spike,
Before finding out about sssd domains I did try that, but messing around with nsswitch.conf to add NIS when authselect is configured for SSSD causes all kinds of issues. ypbind doesn't start up or I get weird input delays on login/shell or gdm taking forever to start up.
I did get it to work once and got getent passwd working based on nis entries in nsswitch.conf, but then sssd would complain about the user and smartcard cert. Probably because it knows nothing about the user. Not sure if this is the case, just guessing; as I mentioned, this is my first time setting up SSSD.
Regards,
-Leon