I use a paraffin heater aboard my boat, but there are a couple of points that need considering. My heater is vented via a proper flue to the outside deck. Obviously this removes the possibility of a build up of fumes within the confines of the cabin. I am told, although I can't vouch for the figures, that a paraffin heater will produce 1 litre of moisture as condensation for every litre of paraffin that is burned. On a cold day if I was to light the heater, close the hatches and close the flue, within a very short time the cabin would be toasty warm, reeking of fumes and the windows and other surfaces wet with condensation.
How all this would effect use in a tent I'm not too sure, but going to sleep in an unvented tent with the heater on would I suspect be a passport to a very long sleep indeed..
Used with care in a vented tent, secure from being knocked over, and turned off before diving into the sleeping bag would probably be acceptable though.
A health and safety expert will be along to shout at me in a moment probably..