9.100 is in beta now.. you may want to go over to the 9.100 beta forum on this site and post this question there in the General Chatter thread ... I've heard that it should be implemented in 9.100, so that's the place to look.
No, V9.1 does not support Sophos on a MAC, the support is for some other function but not anti-virus. I was hoping that the free version for a MAC might be supported in this release, but no.
The Mac support you see in the release notes is for the Sophos Authentication Agent, not the Endpoint Protection -- I too was expecting Mac support in the Endpoint Protection feature in 9.100, guess it didn't make it in.