VeraCrypt is also a fork of TrueCrypt. By definition, that TC was forkable means it was open source. The owners of the code did not intend for it to be open source, but they made it public source and failed to provide ownership of the original code so it effectively entered the public domain. PD + Source Available makes it open source de facto regardless of intent. Because there is no owner, there is no one to attempt a copyright case. It is not that it is not copyrighted, it is that it is uselessly copyrighted. So the source is available and you can use it as you wish, all the factors to make it open source.
That it is anything but open is purely semantics at this point and even the semantics are questionable as to whether or not they would call it open or not. And the fact that it has been forked multiple times supports that it is fully open now.
