you've beaten the game with? My personal record is 4, with 2 reserve tanks. looking back, I wish I didn't get my second Reserve, seeing as how I got it after Ridley, making it next to useless...
Yes. The Mind Laser only checks for the Varia Suit for some reason; the Gravity Suit does not influence the attack in any way. The battle is scripted in a way that the laser MUST hit you at least once to advance the game, which is why a minimum of 3 E-Tanks is mandatory.
It's also incredibly difficult to get to MB's Mind Laser with +3 E-Tanks of energy remaining, particularly because of the Rinkas/Turrets and the Pulse Beam, which comes from her hands when she has 4,500HP (25%) left.