Probably not the best idea since the mealworms may eat anything growing in the terrarium, like bacteria or fungus that you can't see. And that could be bad for your cham. Especially when those left to crawl around start dying and producing more bacteria and grossness for the others to eat. Also they'll probably just hide from your cham or start pupating into beetles and stop wiggling. Better idea would be to put them in a dish or cup in the terrarium so they are contained but still available for your cham to eat. You'll be able to see them so you'll know how much your cham is eating and it's easy to remove them if they die or pupate.