This is an old thread, but will respond in case anyone else comes across it in a search...
This is a known issue, documented in SAS Problem Note 66889 here: https://support.sas.com/kb/66/889.html
(Problem Note 66889: The "Check for Updates" process does not notify you about updates in the 8.3 version of SAS® Enterprise Guide® and SAS® Add-In for Microsoft Office)
In short, if you have EG 8.3 with no updates (8.3.0.103), you will have to use the traditional way (SAS Deployment Manager) to install a newer 8.3 hotfix one time. After that, Check for Updates should work again.
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