I had this situation come up in a recent game.
My chaos opponent charged my Straken supported unit with his plague marines. We read the counter-attack rule, and the defensive grenade rule, and we both agreed that the defensive grenades didn't affect counter-attack. So the ruling went in my favor, but I'm still unsure, and felt a bit of a cheater when we resolved this combat (even though he annihilated me.

).
Did we get it right, or wrong?