It looks like you're mixing apples with Volkswagens.
Your SNMP settings appear to be all well and good
BUT
linux script execution has nothing to do with SNMP.
Orion logs onto the system via ssh using the supplied credentials and executes the script that was set in the script body of the SAM component.
Based on the error message you're getting, I'd say your perl installation doesn't have the URI.pm that the script requires.
infact your use of instmodsh is correct. Now you need to get the URI.pm installed.
A quck scan of one of my linux boxes show many more perl modules installed than what you show.
Since you're running centos 6.5 ( Oracle stole it from RedHat), you should be able to do the following as root on the box:
yum install perl-URI
and that should get the URI.pm on the system and all the dependancies.
Also it would be useful to post the script you are trying to run. It assists people in helping.
Chris