I think Lucho is sending Pedro, Pique and Alves out there to let them play their way out of their slumps. The coach is giving them the chance to show him more, or else they could all be getting long rests after this game. Lucho wants to get Adriano back in game shape ASAP, he obviously is not happy with his other backup FB options.
I bet Adriano will play on the right in the first half, then on the left for the second half. Barca coaches have used him as the first choice option on both sides for much of the time ever since he beat out Maxwell. Lucho wants one FB on his 7 man bench, Adriano is well suited for this flexible sub role, fully able to play on both sides. Except when the coaches move him into the regular starting lineup, and of course also when he is hurt.
OK, Montoya might be last choice fullback on a team with too many fullbacks. At least he makes the bench for Copa Catalunya. Vermaelen can only dream for a role that important.