net localgroup
seems to have a problem if the group name is longer than 20 characters. You can try shortening the group name, at least to verify that character limitation. By the way, net localgroup
uses the pre-Windows 2000 name of the group, the sAMAccountName
AD attribute.
I would still recommend that you use GPO for this, as it will be easier to add the group to the local Administrators group, especially since you won't have to rename your group. Also, it will be easier to remove the domain group from the local group once the need has passed.