The folks who told you that are correct: additional heat will minimize condensation and add a little heat - until the candle burns out, then it probably takes about 5 minutes for the condensation to return with a vengeance (the warm air will hold more water vapor than cold air; the additional vapor will have come from your breath.)
However, what those folks didn’t tell you (probably because they’ve been very lucky, or didn’t want to admit they burned a tent down) is that the safety risk is HUGE, especially if you fall asleep with the candle lit, and move around and knock it over in your sleep.
I’m strongly discouraging you from trying this; the safety risks are too high, and far outweigh any small benefit. This isn’t a traditional v. UL argument; the UL folks who encourage this are, in my opinion, what some of us call “stupid-light.” You can also minimize condensation by venting your tent a little bit: leave the vestibule slightly open, and use any ceiling vents you have.
I’ve never used a candle or other open flame (or enclosed flame, for that matter) inside a tent, and don’t intend to start.