If i use Vampiric Touch together with my Channel Divinity: Touch of Death from the Clerics Death Domain, do i get extra life-steal from the additional necrotic damage?

I'd allow it nased on thematic coolness of the effect, and the channel divinity has limited uses before recharge required so not too OP. But not aware of any "rule" that covers this scenario.

Quote from Sharwyn >>

If i use Vampiric Touch together with my Channel Divinity: Touch of Death from the Clerics Death Domain, do i get extra life-steal from the additional necrotic damage?

 When Vampiric Touch let you regain hit points equal to half the amount of necrotic damage dealt, it can include any extra damage of that type.

While not official ruling, it's also the answer from the lead rule developper twitter

@Aetharion Vampiric Touch damage is increased by Hunter's Mark, Hexblade's Curse and/or Hex - does this include increasing the hp regained?

@JeremyECrawford Vampiric touch—this spell restores a number of hit points based on the amount of damage it deals (half the damage, to be precise). If you increase the damage, you increase the healing.

RAW, I'd say no. Vampiric touch only heals for the damage it deals, not the additional damage of rider abilities and features. At most, maybe this could work for abilities that add necrotic damage because of just a little vagueness in the description, but that is definitely not RAI. 

That being said, its pretty cool to allow at the table.