That is great, because some of the other software that was using the underlying software have licenses only allowing educational and personal use* and hence would most probably not allow the produced models/point clouds to be GPL licensed.
I am a bit happy to see that there are other open source software as well out there these days. When I last was looked at them some 5-10 years ago* there where fewer open source alternatives to the (often prohibitively) expensive (but usually much more functional) commercial softwares.
Oh, and no I have not used them to create models for FlightGear, though the thought have occationally crossed my mind. I was more interested in using them for mapping and for "scanning" smaller objects.
* For example VisualSFM ("free for personal, non-profit or academic use").
** Back then I had not yet started using FlightGear.