Years ago I PM'd an integration with Salesforce. It worked. I've also been involved with Banner, Peoplesoft (now Oracle Campus), SugarCRM, Google Apps, etc. integrations. If Cobek is proprietary, and if you don't have access to the underlying tables of the rdms it sits on top of, then you would need Cobek to provide an API and/or webservices interface.
Moodle's webservices can do much of an integration if the other system supports that (that is how Salesforce integrations were/should be done). A problem with generic webservices is mapping the data from one system to the other.
IMS-LIS has been an emerging standard for mapping data between educastional systems for many years now - lately adopted by Banner and Oracle, it makes integrations easier - if both systems support it.