Is this a general issue with modules - incompatibilities between different versions and the core? I've not got the "Google Sitemaps" tab under the content tab of pages, and would have had no idea that it was supposed to be there if I had not stumbled upon this thread.
Are there any plans to provide multiple versions of the modules to download, since the latest modules don't all seem to be compatible with the latest core CMS download? WordPress.org keeps a history of all previous released versions (it automatically uses the tags to find the versions in subversion) and it is possible to tag each against the core application version that it works with. There way there are fewer surprises.
I'm now wondering just how much more of the administration screens are being hidden from me. Installing modules does tend to leave the admin screens looking much the same as ever.
Edit: or it could just mean the module is not "installed"? The sitemap.xml works for me, but it's not being added to the SiteTree - the total opposite of the OP's problem, I think.