You can take a risk and put them in glass. The reason I advise against it is because there's no way to tell when the bottles are properly carbonated. Sometimes it takes a few days, sometimes it takes a week...depending on temps and yeast health. If you wait too long to put them in the fridge, the bottles will explode because of the amount of sugar in them.
Glass beer bottles aren't meant to hold the kind of carbonation that soda requires either. Have you ever noticed how thick the glass bottles are with store bought sodas?
The only way around all of this is to force carbonate your root beer with CO2 and then transfer it to glass, but even then you'll have a hard time bottling because of the amount of carbonation.