best answer i can give would be all gas appliances should be fitted in accordance with the manufacturers instructions, any required flues should be fitted to the instructions and tested, and adequate ventilation must be supplied.supply pipework to any appliance must be correctly sized so as not to give lower gas pressure than required to burn correctly. appliances must be installed and commissioned by those competent to do so, and maintained regularly
the main point for me with a gas fridge is that you don't want fumes recirculating through the burner, as that will produce carbon monoxide, which is why the manufacturer supplies a flue. If they don't need one the instructions for that model will say so.
sorry if this sounds arsy, but its not something to mess with (and installations contravening the instructions would invalidate your insurance when something does happen)
paul