Hi. I’m trying to setup (installing from latest ISO 4.5.2) VM (at ESXi 7.x.x) with DXi V5000 Community version and use VEEAM to make backups to that VM.
There's sometimes a bit of misunderstanding here. When you get your download you get a serial number in your welcome email that you can apply to the install. Whether you do or not doesn't matter until/unless you decide to purchase an actual license.
But you can't really register unless you've purchased a license. your install is 100% functional and upgradeable (the version you downloaded should have been 4.5 but version 4.5.0.5 is available for upgrade from within the product) my you can't register it per se.
When/if you are ready to upgrade to a supported/paid license we'll be glad to help you out if there are other issues.