I would expect this command to return the gid for this group.
Indeed, while the domain groups are working:
bin/wbinfo --group-info='domain admins'
you are correct to note that, local aliases do not appear to be:
failed to call wbcGetgrnam: WBC_ERR_DOMAIN_NOT_FOUND
Could not get info for group administrators
That's not a highly critical issue but more something that should be fixed eventually.
At a first glance it didn't look like it's too easy to fix it.
this particular issue, that we do not look up domain aliases, is not yet in master
wbinfo --group-info='BUILTIN\administrators' (note the right domain also) works correctly, tested with 4.12