The thing about using regular candle scents in gel candles has to do with whether or not they are "polar" scents ... not to get too confusing with this, simply put, regular candle scents in a gel candle can have a tendency to move through the gel and settle at the bottom of the candle. They don't do this in wax candles, because the wax is stable and firm, but gel is not, so they can sink. When this happens, the f/o becomes concentrated near the bottom of the candle, making it so that the gel that is left at the bottom has WAY too much scent in it than what is safe and it can ignite if the temp. exceeds the flashpoint of the scent.
Although many people still use regular candle scents in gel candles, it's really not the safest route to take ... also, they can cloud your gel ... so, there's the other issue.
I hope this helps!
Kathy