A ProM 6 Package may have a license that is different from the ProM 6 Framework license. If you want to know the license for a certain ProM 6 Package, please start the ProM 6 Package Manager and select the package. At the right hand side, the license will be shown, next to the logo for the package.
If we (as the owners of the ProM 6 Framework) would be very strict, then every ProM 6 Package would have to use a license that is compatible with the GPL license as used by the ProM 6 Framework. However, we are not that strict, and allow developers of ProM 6 Packages to use a license that suits them best. We are only strict with the license if the ProM 6 Framework is used in other applications.