If I recall correctly ALL MODS that are released publicly are the "semi - property" of Bethesda - they could use them themselves without paying anything, probably even without consent of their authors(as bethesda owns anything that has something to game and they only allow others do to things under the condition, that they won't take money for it )
Using the wholly new mod content, made by someone (ie questline, Location, Creatures etc) would IMO not by ethically correct, but using the others' patches, fixes and ideas is IMO wholly ethically just/not harming others.

Is it true?

If so, why does Bethesda use this opportunity (Unofficial Patches, thousads of autonomous fixes, framerate optimizers etc.), use them(I'm not sure if they need authors consent in that case(of course ,with previous testing) and add it via Official Patch.

In that way not only PC players, like me (that need to search for individual fixes) but also console ones(as PC code usually translates directly to XBOX(see modded savegames, probably illegal but I'm proving that it's possible)(probably not PS3 :/) get a consant flow of a bazillion of bugfixes and not an occasional "more new bugs that new fixes patch".

Opinions?

All I'm pretty sure of is that "Build Your Own Home" stopped being worked on after some help from Bethesda.
( And Hearthfire )