If so, is there any way to check for more than just your PostgreSQL instance being up?
This weekend, we had an issue where a database shutdown failed due to a rogue query that would not die w/o a kill -9 being done on it. The database remained up and accepted connections only to tell the connection to go away because the database was shutting down.
This up and accepting connections caused our Nagios instance to not report the database being down.