I have the following LAB setup, 2 x vCenter 6.0.0(Build 3634793) with SRM 6.1(build 3884620) and vSphere replication 6.1.1 (Build 3849281) configured.
I have done the following in one site:
I could then use vReplication and SRM without any noticeable issues, I successfully did a planned failover and reprotect, no issues.
My question is would thus, would this be a supported means to backup your recovery site replication appliance if you did not have a backup strategy in place to backup the appliance?
That wouldn't be supported mainly because it hasn't been tested. Keep in mind, that doesn't mean it wouldn't work.
Have a look at this: vSphere Replication Appliance Failure Prevention and Recovery - VMware vSphere Blog for ideas about what you'd need to backup and how.