Yes, it would raise ambient levels with the tent closed. Enough to make a noticeable difference, maybe. I’ve heard of people doing this. I don’t burn candles at all because it messes with my sinuses. I would worry about the burnt wax in the air clogging my carbon filter. That may be wrong but it was my first thought.

i would be too paranoid of a fire starting

I have a decent glass enclosed candle burning set up for if the power goes out but I think candles might be too efficient, as they don’t really burn much weight in carbon to turn into gas to make it really worth it. Better off locking your gerbil in your tent. You could weigh your candle and figure it out with math…