Current version IPmanager work only with DNS zone configuration files and must be installed into server where DNS server allocated. If IP address have no revers record or name like 'free' (it can be changed) - addres is free and can be allocated to new VPS. Also administrator can configure address blocks for different reasons (projects or primary/secondary ip). If our developer team will add additional checks for find free IPaddress it will we written in changelog
http://ispsystem.com/software/ipmanager/changelog/