Today it is possible to add a field to a registered table or feature class in a SQL Server Geodatabase outside of ArcGIS, for example through T-SQL or with Management Studio. Such fields appear to be recognized by ArcGIS and they appear magically in sde.SDE_column_registry.
But it is not at all clear to me if this is a supported workflow. As far as I can tell, the documentation is silent on whether I can do this or not.
I need it clarified explicitly because I have been told by support, that since this workflow is not explicitly described in the docs, they will not provide any assistance, for such databases, should I ever need it.
The reason why I want to create fields through another mechanism than ArcGIS is that ArcGIS has a really weird mapping of the ArcGIS floating point field types to SQL Server data types. One that is useless for me.
When a user creates an ArcGIS "Double" field type in SQL Server, we do not get a SQL Server "float" field, which I think most would expect. Instead we get the weird, inefficient and inaccurate accounting-style data type "numeric"/"decimal". Same for the ArcGIS field type "Float". This should map to a SQL Server "real" but also results in "numeric"/"decimal".