there are many reasons why gotomeeting may fail when MWG is used in the environment. As far as I know it does not work with SSL Scanner enabled (because it ensures that the SSL connection between client and server has not been intercepted) or authentication.
There is an example ruleset in the online rule set library at https://contentsecurity.mcafee.com/ruleset_library?cat_id=11 . I was able to allow a test meeting by allowing the destination IPs. It should generally allow you access. You can try to add a user/group criteria to the rules from the library to verify if it works, but as mentioned as far as I know gotomeeting can cause problems when used with authentication.
In that case I recommend filing an SR with support to have them check your options.