tgunr said:
A workaround is to rename the group, I changed the group 'admin' to 'sysadmin' and can now specify the 'sysadmin' as I desired.
The "admin" group is group 80, one of the builtin OS X groups and the group specified in /etc/sudoers, so changing its name is a bad thing. It's better to create a new group, and nest the admin group inside, then specify the new group in the ACL.
However, I do have to say that the ACLs are still pretty immature and have some issues. I get around that by using the nested groups which work well.
So, instead of changing "admin" to "sysadmin" simply create "sysadmin" and nest the admin group inside of it. That way, you won't mess with the built in group structures on OS X.