I don't believe editing the contents of the second (or third, fourth, etc.) table is possible if a join exists. That being said, what type of application are you using to consume the service and perform edits? It is possible to edit RELATED tables using functionality available through the various web APIs (Sliverlight, Flex, Javascript). You might need to develop a custom widget to modify the related records assuming that you put relationship classes in place within the geodatabase. Alternative, I am wondering if it might be possible to publish your query layer to a map service and then subsequently publish the individual tables as part of a feature service with Editing capabilities enabled. As an example to this, I have configured a few Flex applications which use the map service for specific operations like identify and search but use the feature service when the editing widget it activated. I just grabbed the layer or table endpoint IDs from the REST application and plugged those into my various Flex configuration files.