how does DCM allocates an IP for a VDS?
IP range is set to a server group.
In case a specific SD is associated with more then one Servers Group, when adding a VDS on this SD via DCM the IP address that would be assigned to this VDS is taken from one of the IP Ranges that is associated with the Servers Groups that include this server.
The IP allocation is done regardless to the Servers Group (and it's IP Ranges) that is associated with the Service Package that was used for creating this VDS.
So therefore as long as a server belongs to ANY server groups that have IP ranges assigned to them, then an account creation will succeed, even if its Service Package is part of a server group that does not have any ranges assigned to it.