Everyone can hit him out of or trade with the headbutt, it’s not hard. Even characters without a rapid fire normal can do it, like Dhalsim does with down-back jab or Blanka with standing short. Some characters don’t need to do this, but everyone can.
And nobody can punish the headbutt on block, it’s safe. The only time you can get hit after it is if you headbutt over a low tiger shot, hit Sagat, and then as you recover fall on top of the low tiger shot.