The vast majority of the airfoils contained in RCAdvisor.com come from the UIUC Airfoil Coordinates Database. These airfoils are covered under the GNU General Public License. This means that they can be used for any purpose as long as you acknowledge the data source and the GNU license.
Some of the data, such as the Norbert Habe (hn) airfoils, are copyrighted. If you intend to build more than three models with the given airfoil, you need permission from the designer.
Like the saying goes, “if in doubt, check it out!”