no, it has nothing to do with being a 'nice guy' - it is about being direct and honest. I know several brilliant people who are completely confident even in areas where they know nothing. The problem with this is that for me to use that brilliant but intellectually dishonest guy, I need to have a good idea of what he knows and what he doesn't. This one guy I know is a brilliant computer scientist, or at least, he's much better than I am. He's not going to deliberately mislead me, but once he gets an idea in his head, to him, that idea is truth - this is fine when you ask him stuff he knows. You get the right answers, and aggressive rhetoric to back it up. He's a great counterweight to salesguys, 'cause he can talk the boss into doing the right thing. However, if you ask him about something he knows nothing about, he will back up his uninformed opinions and half-baked theories with rhetoric that is just as strong.

With someone who is intellectually honest, I can ask advice on a wide variety of subjects, and even if I know nothing of the subject in question, I can figure out how much my intellectually honest adviser knows about the subject in question, as well as what he thinks I should do.

I also know people who are assholes who are also intellectually honest. Really, any kind of honesty requires being at least a little bit of an asshole.