Hello ,
I agree with Mick.
As SBS 2011 a newest Operating System on the Conrner.
As Mick stated, "It is built on Windows Server 2008 R2 and Any product that runs on that OS should be supported, though it may not be "certified" (a full range of tests run specifically on that platform). "
However, why don't you go ahead and Test it yourself.
Incase, if you are going ahead with Installation, I would recommend you to install only Antivirus/Antispyware on the machine.
Let us know, what were the results.
Looking forward for the results of above test.