Not that you should be able to drink blood and have it relieve thirst. The saltiness of blood makes you even more thirsty afterward. One might say that plasma is like 9/10 water or something, and blood is a little more than half plasma, meaning you get 9 parts water for about 20 parts blood. But, keep in mind that seawater is like 96% water, and that's not good enough. Urine would actually be a much better source of hydration than blood for quite a few iterations through your system before the urea and other wastes got too concentrated.
Dried or partially dried blood could be a reasonable food, as people describe above.
Vomit, however, is really just bile, a little acid, and partially-digested food. No reason why you shouldn't be able to re-consume it.
The ethics for civs eating organs shouldn't be specified, but should be part of the randomness in world-gen. This tribe of elves believes that a person's soul is passed through their kidneys. And, it would be too cruel to allow the soul to wander aimlessly outside of a body, so it's important to eat the kidneys of all creatures, so as to not commit the crime of abandoning them in death.
It seems like this would be a good time to make it so that the different levels of prepared meals take, rather than three different items, some amount of SIZE of food. Each simple meal would be say 1/100 the SIZE of a dwarf (since toady said that the scale is about a factor of a thousand now, that would be 6*1000/100 = 60 size units. Perhaps the next one would be 1/80 the SIZE of a dwarf, or 75 size units, and the lavish meal would be 90 units. That's per food item. This way, the very small creatures (like kittens), would be a reasonable snack, but not a good feast. One kitten would certainly not feed three dwarves for months.