I think black should indeed play 9...d6 and allow the transposition with 10.Bb3 (9.h3 to me seems to combine a bit less well with 10.Nb3 for white, but of course that's also playable).

White can of course postpone the transposition even further with 10.Re1 Bd7, but at some point Bc4-b3 is actually going to be a very useful move. Not sure this is the best example, but for example 9.h3 d6 10.Re1 Bd7 11.Nd5!? Nxd5!? 12.exd5 Ne5 13.Bb3 Qa6 (still not terribly clear, of course) - this would not be possible in the normal main line with 9.Bb3 d6 10.h3 Bd7 11.Re1 Rac8, when 12.Nd5 Nxd5 13.exd5 Ne5 is answered with 14.Qe2 fighting for the light squares. When white omits Bb3 this is more interesting for black, because he can win a tempo with 12...Ne5.

In short, I think 9.h3 is just transpositional, but black probably does not have any real opportunities for exploiting it.

1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 g6 5. Nc3 Bg7 6. Be3 Nf6 7. Bc4 Qa5 8. 0-0 0-0  9. h3

This seems to be a less common move.  In Donaldson/Silman's book I believe they recommended 9.  ...Qb4 while in Greet's book I don't remember this being mentioned.  But I tried Qb4 in a corresponence game and resigned after 
10.  Bb3 Nxe4 11. Nd5 Qd6 12. Nb5 Qb8 (I believe this far is mentioned in the book)  but then 13.  Qf3 and black seems to have difficulties.   

So now I do not trust this line.  Looking in my database I see that 9. ...d6 is the other move played here.  Anyhow I wanted to know what people thought of 9. h3 and what to do next for black as it now appears a reasonable move.  I think after d6 things can simply transpose back into more theoretical lines.