When I set {nis/client, nis/server} to be enabled in site.xml, why is it not enabled after install?
If you installed your system using jumpstart, the first time your system boots, site.xml is applied and then /lib/svc/method/sysidtool-system resets the name service according to the sysidcfg(4) file, disables {nis/client, nis/server} and undoes what site.xml has done. This is a bug, see CR 6421535. To get around this, create another service that depends on sysidtool-system which re-applies site.xml.