Hello Legio and welcome to the forums,
Legio wrote:what is the traffic flow when backing up VM's from the esx in datacenter 1 to tape?
There is no backup direct tape backup, since the backup-to-tape job is design as the secondary job to copy existing backup files to tape media.
Legio wrote:Should I configure the physical server in datacenter 1 as a backup proxy and a tape server?
Not a good idea to use the server located in different site as a proxy, because all uncompressed traffic will go from site 1 to site 2 and then back to the backup repository in site 1.
I would leverage Hot-Add transport mode instead, granting some (dedicated) VM the proxy role.
Legio wrote:I want to prevent that backups from the esx in datacenter 1 go through the Veeam server in datacenter 2 to go back to the tape server in datacenter 1.
True. Do you have any local disk-repository on site 1?