Well, they've got all sorts of info about 10.1 Server on Apple's site, so it looks to me like it's out.
As I understand it, Mac OS X Server is and has always been a completely different OS (Think of Windows 98 and Windows NT-- many apologies for making a M$ comparison... lol)-- so you can't update it with a standard 10.1 updater... you'll have to get a 10.1 *server* update. I'm not sure if they are getting those out in the same fashion as regular 10.1-- I'd call up Apple and talk to someone and see what the deal is.