Yes, you do receive a mana if one of your soldier creatures counterstrikes and damages another creature. However, the limit of once per creature per round still applies. So, you can't use counterstrikes to get multiple mana triggers out of one creature. You could also get mana from doing a ranged attack, a zone attack, a doublestrike, triplestrike, or a sweeping attack. In these instances, you still have the limit of once per creature per round, however, which makes the last three pretty rare but still possible thanks to factors such as Daze and Defenses. Like sIKE said, basically if you Declare an attack, it counts as an attack.
