Is it safe to roast marshmallows or hot dogs in a gas log fireplace? What about Duraflame or other fire logs?

Definite no on the Duraflame and other treated fire logs (and the same NO goes for chiminea wood). These are all treated with chemicals and burn into the flame itself - and you will end up eating at least some of it with the marshmallow you toast and eat..

As for the gas logs - your instructions should tell you about that as I am not certain. I tried to find some information, but could not. I would assume that it should be ok as you can cook on a gas grill - I don't think this would be any different...so -- pass me another s'more would ya?