Hello,
At the momment, if you want to assign multiple Resellers the same IP to share, and you want to that IP to not be the server IP, you need to do the following:
1) Assign the IP to the admin
2) Goto the Reseller Panel, IP Manager, set the IP to "Shared"
3) As root via ssh, add the IP to the ip.list file for each of the Resellers who need it. You'll need to do this step for each Reseller you create.
/usr/local/directadmin/data/users/resellername/ip.list
That's it!
John