Plants use Co2 as fuel and a rich supply certainly increases the growth rate no matter what lighting is used. This is especialy true in rooms with poor ventilation. You can have all the lights in the world, but without Co2 then photosynthesis is significantly hampered. Another consideration is that urban air contains about 5 x more Co2 than in rural areas. This is due to cars, population and various home heaters. Who would of thought that smog was ever a good thing! If you're growing in the winter months and need additional heat, then using a gas heater is excellent because the by-product of burning gas in water vapour + Co2.

Basicaly it aint gonna hurt, so try it out and let us know how it goes.