Hi,
Stirling uses the Windows Update Client API to obtain the Stirling updates. SCCM tells the Windows Update Client where to go to get the updates. So as long as the WSUS Server have been configured to download and approve the updates there should be no issues integrating a Stirling deployment to use your existing SCCM 2007 deployment. Here is a link to the TechNet article that explains how to set up a FCSv1 and SCCM shared WSUS infrastructure, the process for V2 is almost identical.
http://technet.microsoft.com/en-us/library/dd185652.aspx
Chris,
Senior Stirling Beta Support Engineer