The Vassal code is licensed under the GNU Lesser General Public License version 2.1 (LGPL-2.1) and therefore allows third-party use. Individual modules may contain materials, such as graphics and the like, that is copyright of third-party, and which gives no license to third party. In that case, it would not be permissible to distribute those materials to third-party - be it an A"I" or similar. Individual projects should stipulate under which conditions their materials can be used. If no explicit license is given, then one cannot assume that one has license to distribute.
Yours,
Christian