I would recommend checking all certificates on every host locally too, as you then can catch other than HTTP certificates too, like IPSec and OpenVPN. I found a good plugin on GitHub that does just this. If you then just put your certificates in the proper directory you can have them all checked and monitored by Nagios. I use nagios check_http to verify that a page is actually serving content via SSL.

https://github.com/kumina/nagios-plugins-kumina/blob/master/...