I understand this post was made in 2017, but I recently purchased Sims 4: Vampires and had a similar question.
I was taking the route of asking sims for a drink while feeding my vampire and was trying to figure out if I befriended a human Sim, if they would be more comfortable letting my vampire drink from them. I thought that would make logical sense considering it would prevent the vampire from violently uncontrollably drinking from them which would happen eventually, and it seemed reasonable that friends would learn to trust each other not to kill them. I quickly found out this is not the case. Asking for a drink doesn't usually go well, regardless of their relationship. As the first post points out, a human Sim cannot offer a vampire a drink on their own, which seems like a reasonable friendly interaction between friends, even if their relationship status had to be pretty high before they could do so.
The other idea I had about unlocking this interaction is through learning Vampire Lore, considering both vampire Sims and human Sims can learn about vampires through research. The Vampire Lore stuff explains how vampires live their lives including how satisfying thirst works. Human Sims could learn how to offer a drink to a vampire and maybe even how to cope with being bitten better, instead of just learning how to use garlic to keep vampires away.
Either way, it would be awesome if human Sims and Vampires could get along like this. Right now it's like human Sims are only tolerant of vampires if they act like humans, which is basically asking them to just not be a vampire at all. It's a reasonable reaction for just meeting a vampire, or not knowing much about them, but it is as if human Sims can't ever really accept vampires for being different.
Recap of helpful additions between vampires and humans:
Allowing human Sims to be more open to being asked for a drink based on friendship level or Vampire Lore knowledge
Allowing humans to offer vampires to drink from them based on either friendship level or Vampire Lore knowledge
