No, I think their data centers are filled with thousands of 1U blades attached to a boatload of storage. The OSs they run probably run the gamut of what’s available and what makes sense for the specific functions of the servers.
AIX/Unix and yes, even windows.
Take a look at some of their job postings for their data centers.
If Apple is indeed ready to turn its sights back to the enterprise, you can be sure that the boys in Redmond won’t be taking it lightly.
I don’t see them running anything but their own gear on the front end stuff in Apple HQ. Do you?
I doubt if Jeffrey Snover is losing any sleep over it. After the XServe debacle, it'll take some convincing to get people back onto that bandwagon. It appears they've given that up in favor of consumer entertainment appliances.