every other weapon with lifedrain proc from previous tiers benefits from spell power
-Wraithsycthe,
-Shadowstrike,
-Ancient Hakkari Manslayer
Neretzek, The Blood Drinker, is currently bugged not getting sp bonus, while it should,
you can watch an old vanilla video here in my bug report about it
Neretzek, The Blood Drinker spell power scaling