Free software on the market (like Gabest filters, Haali, ffdshow) can be used in any circumstances, AS LONG as money are not involved. You can't sold a comercial program that it's distributed with free software because you will violate the law.
As long as BSPlayer uses DirectShow and the filters that are programed to use DirectShow, and those filters are free, you can't implement them into the program. On the other hand, you, as an end user, you can use them. As for the DVDs, if you sell a program that can play DVDs, you must pay royalties for that. And will pay even if the team will build from scratch BSPlayer's own filters and splitters. Same thing with the new DVD formats (BR and the lately HD-DVD)
And, if I recall corectly, FFDshow can't play MPEG2 (DVD / BR format). As HD-DVD it's dead, I think we can skip it.
http://en.wikipedia.org/wiki/GNU_General_Public_License
I hope someone from the staff will come up with more precise informations about that.