It might wriggle off the plate. Then again a white plate may blend in with a white rat... I have seen pics and vids of snakes eating on the mulch and even cypress mulch with out problems but every so often we will see a post here about a snake getting some bedding stuck in its mouth. It can be removed but tricky. I never had to do it myself since I use news paper for bedding.
You could always remove the animal and place him in a seperate box and feed him there. Just stick him in a vented shoe box like a sterilite 6qt (I think, its been a while since I used em so I am not sure of the numbers) with a live rat chub in a dark area for a couple hours and see if that works