...
The standard license of the tool includes the MigrationSupport.dll assembly that you may use in binary form with the upgraded code However, if you want to be able to modify the MigrationSupport code, you should purchase a license for the source. A perpetual license to the C# source code of MigrationSupport.DLL is available to gmStudio customers.
Note, we have a "branding tool" that will rename the code and files used in the MigrationSupport namespace so that they may be consistent with your organization's naming standards.Here is the official statement regarding Runtime Library Requirements and Support
https://portal.greatmigrations.com/display/GMG/Runtime+Library+Requirements+and+Support