In WAS you can use a fail over server but it needs to be a copy of the primary which is the case for you. WAS will then use it should the primary be unavailable. I have configured this for a customer but made them aware of the shortcomings.
With the Community server the same is not true. You can add multiple LDAP documents in stconfig.nsf BUT they need to be different LDAPs more precisely they must not have the same users in them. This is a problem for you.
The only way for this to work for the Community server is using a load balancer or manipulating DNS on a failure or round robin both of which are not terribly reliable.
The problem is that you added to the SSC both LDAPs. You should have added your primary and then from within the SSC gone to security - global security - user account repository - configure - Repository identifier - Failover server used when primary is not available - Add and added the DR LDAP.
You'd be best to back up wimconfig.xml before you make this change.
Remember that this will only work for WAS apps servers and not the community server. It then begs the question, why bother if you have a load balancer you can use? If you haven't got a load balancer then the workarounds will need to be applied to the Community server.
You've got yourself in a bit of a mess but the approach you're taking seems logical.