Sure, but not only : any java source code can be edited with a text editor
Actually, that's not an issue. Source code is correctly defined in the GPL as the preferred form for modification, irrespective of what such form is.
The fact that such software can't be used without running non-free software is an issue, but it doesn't affect the freeness of that copyrighted work. It's like free software packages that only run under Windows or MacOS.
The fact that it cannot be modified with free software is an issue, too but, again, it doesn't affect the legal status of the specific work.
I agree that if such source isn't even readable without non-free tools (because the format is undocumented or whatever) we have a serious issue, but it's about the environment where such work of art is designed to live, not about the status of that specific work.
It is the same as free documentation or free drawings written with proprietary applications. The .doc or .ppt formats aren't really useable in the free world -- I don't care that some companies spent many man-years to be more-or-less able to read them: this is just a very expensive workaround and the situation is still the same as you describe.
/alessandro