It sounds like a decent way of getting a reasonably accurate temperature using only things you might find at home, but I'd want to at least use an oven thermometer to calibrate the oven temperature a bit before trying DMT on it.
Also, don't "throw DMT over it" , carefully weigh out the dose you want, put it in a little paper fold or small spoon, and tip it onto the plate once you're ready with a funnel (or bottle with the bottom cut out) in your mouth to capture the vapours. It'll likely vapourise quickly in one short puff, so you need to be on standby to inhale it.
I guess you need to consider the physical safety aspects too, you don't want to slump unconscious onto a hot metal plate!