M.P.
Heat may release chemicals but once the plastic is cool the chemical fumes are gone. I'd use it.
The reason to wash plastics on the top rack is to prevent them from melting when exposed to the hotter heat on the bottom. I wash much of my plastic on the bottom rack because they don't fit on the top rack and have never had any difficulty.
BPA free plastics will not release harmful chemicals when heated. Allegedly its the BPA that is harmful and so if it's not in the plastic it can't harm. I, however, do think the whole plastics thing being harmful is a bunch of hype. One is not exposed to enough of the chemical for it to be harmful.