[This podcast with one of the pilots answers just about every question on the shuttle carrier you could have and it's worth a full listen.][1] But to cover the flight dynamics I would skip to 50:33 minutes, where the pilot states (please note there is no official transcript of the podcast and I typed this as I listened to it, please see the official podcast for the actual verbiage, but this is close): 

> **Markus Voelter (Interviewer):** Let's talk a bit about the flying characteristics, did the wings of the shuttle add some extra lift or
> was it mounted with essentially 0 angle of attack?
> **Arthur C. “Ace” Beall (Pilot):** It was mounted with some angle of attack, you can see that as it's sitting. At the speed we were flying,
> the carrier itself was about 5 degrees nose high. The shuttle was creating lift, but
> how that affected it aerodynamically is hard to say, it was always
> mounted the same way so we had no basis of comparison. It did, however,
> create a lot of drag and made the aircraft very top heavy so bank
> angles were limited.

So some lift was generated but at the speeds they were flying, other limitations came into play that were more of a concern. It's also worth noting that when in transport no one was in the space shuttle and the control surfaces were not used in any way. 

  [1]: http://omegataupodcast.net/195-flying-the-shuttle-carrier-aircraft/#t=49:50.503