I think he was vaguely familiar with his stuff, because he did major in anthropology for one year, and that's part of the genesis of Star Wars since he studied a lot of mythology and cultural practices. But the whole notion of Campbell basically "providing the roadmap" or whatever is total BS. But, he may have skimmed through some of his stuff since one of the case studies in Hero with A Thousand Faces shows up (supposedly, but its not a real match--Massai in Campbell, Masasi in Lucas. Personally, I think Lucas got this from people he met, like he did for all of his early names, since Masasi, like Vader, is an actual surname). The personal connection between the two men doesn't even begin until after Star Wars, I think around 1981 was when they first met.

He did have a copy of Hero on his writing room desk in 1981 when he was doing the rough drafts of Jedi, but that may have been there because they had recently become aquaintences and so he maybe took a closer look at his work.

I share Lucas sentiment in that Campbell was far more powerful as a speaker than a writer. I can't stand his books; I sold my copy of Hero a few years ago--it had Luke Skywalker on the cover actually.