...following on from above, are those separate domains too? If so, you will then need to create a user account for BEWS in each domain, and add it into the correct groups (Domain Admins for eg.). Once done, add each of those user accounts into the BEWS media server under Network.
If there are trusts between those domains, you can look at using 1 service account for them all, and just adding that specific service account in the correct groups on each domain.
If you are unable to resolve those IPs --> Names on the servers, you can add in entries into your hosts file on your backup server, pointing to those servers.
Don't forget to open the correct ports on any firewall you have from between the subnets.
Laters!