I assume that you mean serverSelectionOrder in the RFA configuration.
According to the RFA configuration guide, if serverSelectionOrder is true, servers in the serverList are chosen randomly instead of from left-to-right. Therefore, It defines the behavior of RFA to select the server in the serverList when failing over.
In addition, serverList specifies a comma- or space-delimited list of hostname[:port] combinations which provides redundant source applications to which RSSL_Cons_Adapter connects. It provides the failover functionality for the RSSL connection. The redundant source applications in the list must have identical sets of user interests: user entitlements, login attribute information, available services(s), service capabilities, item availabilities, etc.
In conclusion, ADS in the serverList must use the same set of user permissions (DACS) and provide the same set of services, service capabilities, and items.