Hi Mike,
Yes, excel allows multiple connections per Excel Sheet. We can create a separate connection for each workbook in an Excel sheet.
However, you will need to manually merge the sheets after publishing. After publishing the reports, open the both reports in excel. Right Click on workbook name and use the Move or Copy Option in the workbook merge two excel sheets. This will also move the data connection of the sheet to destination excel sheet. You can see the connections on Data tab in excel sheet.
If you make any changes in reports in GP and re-publish them, you will need to merge the sheets again.
Rubal,
http://dynamicsgphelp.com/