Where is the sudo group or is it replaced by group wheel
The group admin is synonymous with the group sudo found on Linux boxes. Members of the group wheel have a special privilege where they can su (switch user) to root assuming that the member knows root's password. Since the root account is disabled, membership in the group wheel would be similar to membership in the group admin, if configured in /private/etc/sudoers. Since some Apple supplied command line tools require admin membership, the group wheel is a vestige from FreeBSD.