Yes, influence is everywhere and anything we read spills into it. But The Hobbit is almost consciously a retelling of many elements of this earlier book, particularly in the playful, riddling language of The Hobbit, which is not (as much) shared by the LOTR books, much less the Simarillion. Tolkien is many things, to be sure, but The Hobbit is trying hard to be the kind of book he would read to his own kids, a kind of bridge to the world of myth and legend that LOTR ultimately became. Tolkien borrowed gracefully from this earlier work in figuring out how to balance his love of language and myth with the simpler, more immediate demands of storytelling. MacDonald showed him how to do it, and without him, we would have never had the 'human' element of LOTR represented with Frodo, Sam, etc., and which is so necessary to step into that world as a reader. So in that sense, the influence is more one of storytelling than in subject matter. I don't think it's too much to say that MacDonald taught him how to write to children--meaning, he taught him to write to the 'eternal child' in all of us, whcih is what makes Tolkien's best works so universal.