Updating a NULL geometry using ArcMap fails when the data is stored using SDEBINARY and the feature class is non-versioned.
This is a known issue.
When updating a NULL geometry for a non-versioned feature class stored using SDEBINARY, the value for the spatial column in the business table is set to 0 while the feature and spatial table's fid values are set correctly. The result is a record in the business table with no corresponding geometry.
Additionally, if the editor attempts to update another geometry the value for the spatial column is again set to 0 violating the unique constraint.