You practice diminished scales. You play the practiced scale in your improvisation. Unless the material is Brazilian music, which calls for a diminished sounding line, it will sound too diminished, or too practiced. When you listen to giants like Miles Davis, you won't hear such a line.
Besides, as explained in my Jazz Theory Workbook, figuring out the correct scale in the tonal context isn't easy for sight-reading. Here is something I came up with when I am in that situation, and it works well.
Read on…