If you are playing in a tournament then it is always up to the coordinator. If you are playing a pickup game then refer to the codex. The Dogs of War rules state what armies can take them so as long as you stick to that they you are fine. As for the allied contingent rules I believe they are opponents permission, but if your opponent will not allow you then they are not worth playing anyway. The Dogs of War rules are in the Warhammer Chronicles books or floating around in a PDF on the net. As for the allied contingent rules they may still be on the GW site so check there.