the tool is returning an OWA time zone, but even after manually modifying the time zone properties from my outlook client, the tool is still not picking anything up for the OutlookTimeZone.

Q: In my test case, the tool is returning an OWA time zone, but even after manually modifying the time zone properties from my outlook client, the tool is still not picking anything up for the OutlookTimeZone
A: Do you know where your users are in respect to time zone?  If you have one time zone per server then you should be able to manually set the time zone data via editing the MSEXTMZ.ini file in excel and setting the time zone to one value.  if you have no other information you could use the OWA timestamp if it looks accurate.

For details on editing the can edit this file in excel: See Time Zone Extraction in http://support.microsoft.com/kb/930879 for details.