it does. took a minute to load a single player game, set starting level at 10, me as oak. Got rank 3 divine justice and maxed out penitence just to destroy mana. When you see the green numbers flash up, it's both hp and mana. (Always thought they should add blue for the mana since health bar is green and mana is blue.. but w/e). You can easily see the mana jump up in this test (lvl 10 oak with no mana items still only has liek 1600 mana.. and killing a creep gave me ~70 hp / mana).
Personally, I like to just grab 1 rank of this at level 2 to allow me to stay in the lane longer and hopefully get some hp / mana back faster.