Hmm, Casper has that feature but I can not recall seeing it in Profile Manager. However, can the "Restrict App Store to software updates only" setting in the Restrictions payload get you want you need? Unless the users are purchasing apps, this may be the way to limit visibility to the new OS.
Now, the other option (have no idea if this will work) is to check the "Restrict which apps are allowed to launch" and then adding /Applications/Install OS X Yosemite.app/ to the exclusion list. The app is a folder after all.
Now, the challenge though is that checking the box also activates the Allow Apps array. It is possible that having no apps in the list will deny all apps from running. Test this on ONE machine first to ensure proper implementation.
Sorry, have not needed to do much with restrictions. When I do, I have Casper to handle the task.
Reid
Apple Consultants Network
Author "Yosemite Server – Foundation Services" :: Exclusively available in Apple's iBooks Store
Author "Mavericks Server – Foundation Services" :: Exclusively available in Apple's iBooks Store
Author "Mavericks Server – Control and Collaboration" :: Exclusively available in Apple's iBooks Store