The install of OS X Tiger Server I currently have in the house (to learn it, we actually have a few customers running it that) selected HFS+ as default and nothing has balked yet. The UFS choice was there as well, but not preferred. So it looks like that did change. Keep in mind OS X Server 1.0 before the OS X client shipped was a very different product then what is out now. It was much more a hybrid Mac OS/NextStep type product.