Does "Heal Block" block absorption moves such as Drain Punch, Giga Drain, Leech Seed, ect.?
In Generations IV and V, HP-draining moves will deal damage but not heal the user. Starting in Generation VI, HP-draining moves cannot be used at all while Heal Block is active. The only exception is Leech Seed.
Heal Block (Bulbapedia)
>Draining moves (eg. Giga Drain) will cause damage but will not heal the user.
Yes, it does.
Source