Others have tried it, I believe with mixed results. When its removable it allows grease below it which will give you more to clean and it allows a path for the grease to get to your firebox if you don't install grease dam.
As for using it as a grill. I personally think the coals would be to close to your cooking grate in a typical reverse flow smoker. They are typically 4" (give or take) away from the grate.
Most suggest using your smoker as a smoker and build a separate grill for grilling. I do believe some folks have had some success with a grill over their fire box.