Not identifying minions to players opens up your combats to the possibility of tactics being decided by nothing but random chance. I think the dice provide enough of that element already.
Imagine entering a room with two groups of Orcs, one to each side. One group is standard even level challenge of 5 critters and the other is 5 minions. If the controller goes first and blows his AOE daily on the standard Orcs thinking they are minions, it might do a measly 10 damage to each and more importantly, the minion's are going to swarm around the party and become very difficult to kill in mass, suddenly making the encounter far more difficult than if he had guessed right. The character was unable to perform his role for no other reason than the DM set up a 50% chance for him to fail to be able to identify the targets his class is made to deal with.
Now 5 rooms down in the dungeon you might come upon the exact same encounter, only this time the minions and 'real' creatures have switched sides of the room with no way of the player's knowing. It's pretty lame.
D&D combat has always had as part of its strategy that players are going to learn about the powers and abilities of different creatures, including how hard they are to bring down, and use this knowledge to deal with threats more effectively. To use minions in a way where they are sort of like mirror image doubles of real and challenging foes, is just asking for trouble.