No, setgroups() would be appropriate if syslogd was started with -g GID. Yes,
then syslogd() should do "gid_t gid = GID; setgroups(1, &gid);". Otherwise,
if syslogd() was started without -g, it should call initgroups(). In this
case you want to control the group permissions by /etc/{passwd,groups} etc.
and it might be necessary to put syslogd into more than one group.

BTW, in your example, syslogd would have wheel as GID, right? That's
probably not desired.

-- 
Christian