I posted about this to the developer of the plugin, but it seems to be more of a Nagios issue. The plugin reports OK, both on the command line and in Nagios, but it appears in yellow as a Warning on the services page.
./check_oracle_health -v --connect=oracle_user/oracle_passwd@mySID --mode=connection-time --warning=3 --critical=8
OK - 0.14 seconds to connect as oracle_user | connection_time=0.1437;3;8
SERVICE ALERT: oracle_host;Oracle mySID Connect;WARNING;HARD;3;OK - 0.14 seconds to connect as oracle_user
Current Status: WARNING (for 0d 1h 15m 37s)
Status Information: OK - 0.16 seconds to connect as oracle_user
Performance Data: connection_time=0.1550;3;8
Current Attempt: 3/3 (HARD state)
Last Check Time: 06-22-2010 15:31:44
Check Type: ACTIVE
Any idea how I get Nagios to report it correctly?