Hello,
If the servers are hidden from the Network neighbourhood, then they will not be visible in Backup Exec selection list.
However you may try backing them up using User Defined Selections and verify the results. Refer the following technote.
Title:
How to create a user-defined selection in Backup Exec 9.x and 10.0 for Windows Servers
http://support.veritas.com/docs/254193
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