The WebUI site did gather, so the Deploy/Update fixlet became relevant. The client on the WebUI server was upgraded to 9.5.7 prior to executing the fixlet. Based on what you are saying, it shouldn't matter if the database configuration was set while still on 9.5.5 or after the upgrade to 9.5.7.
Support asked if the WebUI install requirements were met. My DBA assures me that they are. My service account has full DBO. The gap appears to be a missing WebUI schema. There are three WebUI-related tables, but not a schema per se. It isn't clear where it ran off the rails.