Just checked the knowledge base article: http://help.filemaker.com/app/answers/detail/a_id/7152/kw/system%20requirements
We have server 10 running on Server 2008 and I remembered checking this info when we were selecting a new server to install it on.
Windows Server 2008 Standard Edition SP1
is listed. R2, a later update is not, but we've been keeping updated and aside from the annoying "deaf server" bug that is still with us, has run quite normally. We are planning to down grade this system to a "vitual" 2003 release as we have an indentical install on a 2003 edition that has never once gone 'deaf' as a test to see if it makes a difference.
Plan to post back to the forum what we find out after we've made the change and run it for a while...