Kills using Serpent Strike and the relic enchant "HP and Suppression gained on Kill equal to 100% of the killing blows damage"  does not heal on kill.  Missing Suppression has also been noted in a prior bug report.

Easily tested by loosing health and only using Serpent Strike on multiple group and individual enemies.  No heal is given despite how many enemies are killed.

Note: Not referring to kills from poison DoT but kills from initial blow.