Postgisraster is not supported in ArcGIS Pro at the moment. Only ST_Raster with SDE works properly.
We propose to enable Postgisraster support in ArcGIS Pro both for in_db and out_db rasters (see definition of in_db and out_db raster here). PostGISraster has one big advantage referring to database management. Rasters can be kept outside the database as referenced geotiffs in consequence the size of the database is a lot smaller than storing rasters inside a database.