The chance of a burning candle starting a fire in an RV is no worse than in a regular house. Burning candles start fires due to careless use.
It's not a propane or gas thing it's purely if the candle falls over or a curtain touches the flame or it's too close to another flammable source a fire may start.
We use candles all of the time in the RV and at Home. In the RV we use them to help save on battery power when boondocking. We will place candles in strategic locations to provide enough light to get around inside without stumbling.