What you're trying to do will work provided your DR 'bubble' network contains the backup software/devices.
The only thing I'm not sure about is automating a test failover.
Essentially that's what you'll need to run in-oder to power up all the protected virtual machines in the DR site without actually failing over.
Just to be clear, I've used the term 'bubble' network but as I think you've indicated you need an isolated network which will be used by all the virtual machines and the backup devices, this is different from the 'bubble' network which VMware creates by default on each ESX host.
In theory, the replicated data to your DR environment is a backup (in a way). I think I understand that you pretty much want ot test SRM to test bubble and perform backups there. If your backup server is on your test bubble, I don't see why it can't work. However, I pretty sure this is not a recommended method for backups.
You could use VDR to take snapshots of your VMs (no disruption) and have backups of your prod environment available.
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I would not recommend this.
If you are worried about impact is it network related?
If so have you thought about a seperate network for back so this will not impact on production.