The disaffected Republicans are generally more of the conservative stripe.
Moderates like McCain.
I don't see any reason why a conservative would vote for the very liberal Nader, except as a protest vote.
I do wonder, though, if Nader isn't a closet conservative.
I've wondered this as well, but it really doesn't matter.
I don't think Nader will draw many votes from anyone.
For one thing, Nader is older than McCain, and some are questioning if McCain is too old.
I also don't think there is a segment for Nader to capitalize on that is not better answered with another candidate.