and put "REQUIRED_INTERFACE=<hostname>" to bp.conf of the client or its equivalent in Windows Client Properties.

Mouse is right, but you may also need to add static routes to the client, if our master/media  server is more than one sub-network away from the client, else data will be send via the default gateway.

Doing a backup on a different NIC is a good consideration, but also consider putting that backup data on a VLAN back to the Master Server, so it is entirely segragated from the production LAN.

We have that setup.

For example:
Server hostname: fred (NIC#1)
NetBackup hostname: fred-b (NIC#2)

So any reference in NetBackup we use the fred-b hostname as the client. We also maintain local hosts file entries for this client and the master server which also has a VLAN IP address.

 Stuart has the right idea here.  I have found that once you start introducing static routes, you need to be careful so you remember what you did 2 years from now when someone has a problem and cannot figure out why it is not working.  Leave the hostname alone and add the new version of the hostname for backups, like Stuart shows.

Please do remember that big VLAN's are exposed to spanning tree protocol issues. For larger networks go for IP routing

Some of the cost you take when configuring a dedicated NIC for backup traffic are:

• Static routes (Sorry - But you can't avoid them unless you have a flat network structure)
• REQUIRED_INTERFACE entries.
• alternate client names e.g host-bu
• Performing restore must be done with alternate client.
• Database backup (MS SQL, Oracle, SAP etc.) has it own set of issues.
• Issues for separating real traffic from backup traffic (E.g making sure Windows only register with one name i AD)

And what about jumbo frames should they be also be configured when planning for seperate NIC for backup??

Jumbo frame support need to be configured simulations, what's impossible in our company network. If you have the ability to configure switches and routers for jumbo frames, go for it.