vCenter is vCenter. None of them support multi-homing until 7.0. Windows vCenter is dead anyhow, so no point upgrading to it.
vCenter does not install the VDDK. That is a set of client libraries used by your backup application. As I told you before, VDDK versions are in step with vCenter versions. vCenter 6.5 will bring the level of VDDK up to 6.5.
Sorry I'm so heavy but I need to understand all of this in order to migrate.
We have the verison Netbackup 8.0 that is compatible with vddk version 6.0.2 that is compatible with 6.5u2.
But as you say the Vcenter is equal to the vddk 6.5. then will i have to migrate to Netbackup 8.1 ??