Yes of course you are free to use these to do any of your own work. I have no problem with people making hybrids, the only thing that really I object to is making copies of inbreds simple F2 generations and then listing those along side by donating them to SB or the like.
If you want to actually put some real work into developing your own line, and do some real inbreeding where you grow a bunch of the originals and do some real work selecting within the line for a few generations, than have at it. To me this is more more acceptable then simply taking 1-2 plants from a 10 pack and mating them together, to then be sold on the same shelves... that grinds my gears a little - but if you want to actually put in some work and do some real breeding, who am I to say no? I support anybody that wants to put any actual breeding work in, once the genes are out there, they are fair game afaic. Part of the point of releasing say the Bubba cross, is so people can use those as a start of a backcross program to the Bubba- these simplify the work as you already have positive pollen inputs to stat the backcross line. Heck I'd probably trade you for some of those also, just to have them in the library- I save you a generation on the F1, you save me a generation on the backcross. Seems fair.
Have fun and use them to make something great or better than the originals, and if you are doing something positive for Cannabis and not just your pocketbook, I'm stoked.