No, it is not possible to directly edit Query Layers (in any database) using the standard graphical editing tools of ArcMap/arcpy (as if they were shapefile, file geodatabase, or enterprise-enabled feature classes). The underlying ArcSDE technology is the mechanism that permits both versioned and non-versioned editing of database tables -- No ArcSDE, no editing.
There are, however, two ways to indirectly edit database tables within the framework of Query Layers. The first is to use a Feature Access enabled map service (an ArcGIS Server feature service). This mechanism requires you to publish a Query Layer MXD to an ArcGIS Server host with "Feature Access" enabled, which provides the write capability REST service (to which Desktop tools and web APIs are clients):
See this blog post for more details on the evolution of Query Layers.
The second way to edit Query Layer data is not for the faint of heart: Use a SQL database cursor via
arcpy.ArcSDESQLExecute to send
DELETE SQL statements directly to the database.