I know this post is ancient, but I just thought I’d add:
In modern versions of ArcMap and ArcGIS Pro, it’s possible to register views with the GDB and publish those views as map services.
My experience with views that have a calculated shape column is: ST_GEOMETRY views are slow, but SDO_GEOMETRY views are fast. Also, XY Event layers are surprisingly fast too.
Something that might be of interest to Oracle people: function-based spatial indexes. If you are a data creator/owner, then you would have the privilege to make regular Oracle indexes. And if you can make regular indexes, then that means you can make function-based indexes too (via a SQL client like SQL Developer, Toad, etc.).