I am not sure if I get your scenario correct.

Are the server ABCD servers to be backed up?
If yes, then it is not Veeam's way for this. You don't attach a tape drive to the servers you want to backup. The tape library and the taoe drives are connected to a Veeam taoe server (this can be the Veeam Server itself or an own Windows or Linix server with Veeam's tape server role).

Please see the best practice guide for further information.

https://bp.veeam.com/vbr/2_Design_Structures/D_Veeam_Components/D_tape_server/tape_server.html

As @JMeixner mentioned above, are you able to clarify a bit more? 
Essentially, the way Veeam works is that you would  need to deploy a Tape Server role that would connect to the Tape Drive itself. 
Once this has been done, you’d then be able to take a backup of the servers and then write those backups to tape. You also have the option for direct Backup to Tape via the NAS backup option. 

Veeam requires exclusive access to tape drives so be aware of that. If there is one robotic arm I find sharing does not work well. You can try to partition the unit and zone one drive per server then have three tape servers in Veeam but I cannot say it will work 100%.

Oops.. I missed some points there, ABCD are the tape servers

While I am searching some points about tape servers, wondering these two statements:

1. VMware does not support tape drives connected directly to ESXi 5.x and later

https://helpcenter.veeam.com/docs/backup/vsphere/tape_supported_devices.html?ver=120

2. Deploy a dedicated tape server. As a tape server, you can use a Microsoft Windows or Linux server, physical or virtual

https://helpcenter.veeam.com/docs/backup/vsphere/connecting_tape_devices.html?ver=120

Is there a contradiction for deploying a virtual tape server?

You can deploy virtual tape servers but I have found them to not be good and flaky. Physical is best for tape.

Virtual tape servers or tape drives on VMware generally are possible, but not advisable. There are a lot of problems.

You have 4 tape servers in your scenario. You have to have either 4 libraries or a tape library that you can logically partition into 4 libraries, because you cannot connect a tape library to multiple tape server.

You can select a server in Veeam and make it the tape server.  You said Tape Library. So that tape server would talk to the library. If a drive fails, the other 2 would still be available. Any server and use any drive. You will get the best use this way not having idle drives and others with queued jobs.

If you wanted, you could have a few tape servers each with their own drive, but that would involve stacking up another server for Veeam. 

If you are using fiber, connect the fiber host to the FC switch install the os, zone the drives to the host, configure the drivers and add it to Veeam.

the 1:1 server to tape solution doesn’t provide high availability or concurrency.