Pam_wheel defaults to use group root, not wheel, if the group= parameter is not used. Contrary to doc. The syntax in the doc is also wrong. It refers to the old /etc/pam.conf configuration file, not /etc/pam.d/*. /usr/doc/pam-0.68/txts/pam.txt: "This module is used to enforce the so-called wheel group. By default, it permits root access to the system if the applicant user is a member of the wheel group (first, the module checks for the existence of a 'wheel' group. Otherwise the module defines the group with group-id 0 to be the wheel group)."
This was also reported and discarded as bug #921. Since the code now checks for WHEEL_IS_WHEEL, that flag should be defined to make the module work as intended.
Fix pulled from current Linux-PAM tree. Will be fixed in next release.