In some cases, yes; if an event or exhibition has a sign that says "fri inngang" it means that it's free of charge.
Having said that, "gratis" is the most common and often the only natural sounding option. I would not take the example sentence, "Er de frie?", to mean "Are they free of charge?".
The word "fritid" is used to denote free time. The website has more info on compound words than the app. There are also more discussions about the differences between free (as a people), free of charge (gratis), and free time (fritid). I keep the app and the web link in a folder on my home page of my phone to make jumping back & forth easier.