It isn't therefore a heal. HOWEVER, if your teammate is affected by Shivas they will regain less health. I assume this works the same way for Skadi and Spirit vessel but I'm not getting paid to test this.
HOWEVER HOWEVER, it IS buffed by spell amp.
Wraith King on the left side of the screen was healed without the amp from KayaSange, Wraith King on the right side was healed with the amp. Life drain was kept level 1 so it could be used for one full duration without taking either of them to max HP.
In conclusion, spell amp good on Pugna, Holy Locket not so good but still useful for the item itself. So, Pugna who stood in the back last night healing me but refused to use his Holy Locket charges on me, I dislike you.
ALSO, spell amp, on Pugna, also increases how much mana you restore to you allies when you siphon mana instead of health. This is NOT affected by Shivas.
Also can we have numbers which are buffed by heals show their changes when ALT is held down? C'mon guys it's been a couple years already since healing amp came out.
Source: https://www.reddit.com/r/DotA2/comments/ukbjs7/pugnas_life_drain_not_buffed_by_holy_locket/