Actually no, the units will not follow the commander into battle, and I'll tell you why because it's a frustrating mechanic.
By the 4th round of combat, when that commander starts to think about moving, he will in fact be completely surrounded by his men. He will have no empty square to move into, and so will not move - and neither will they.
If you want the commander to lead the charge, then you need to understand some things. First, there are 8 squares that a unit can move into at any given point (unless it flies, if he can fly you are good to go). If the troops are human size 2, then that is 24 men that can crowd into the squares adjacent to the commander. Thus, you can make this work most of the time by having the Guard Commander squad consist of 23 or less men (so he has somewhere to move), and having them start just behind him (so they will move forward to get close, and you maximize the odds of his open spot being in front, as he may not move if it's behind him). The trick is to get the other squads to come with. If you aren't worried of getting blitzed in the first few turns of combat, then you can gauge based on the units' movement speed, how far back to set them so as to be in a line when they all start to move forward. So say it is a heavy infantry with 6 AP. They will start to move 2 turns before the commander, so at 2 AP per square, you want those squads to be placed ~6 squares further back from the commander. Then, you tell then to Hold + Attack Rear, and they should advance straight forward, maintaining a bit of a formation.
Hope that helps.
