Can vampires drain non-sentient beings or monsters?

Question

D&D 3.5e vampires canonically don't need to eat, sleep or breathe. However, they also drain levels and Con (blood), and doing this can turn their victims into vampires or vampire spawn.

I also saw rules in a supplement that vampires can be compelled to use their drain abilities. (Libris Mortis, P8-10)

My question is, can vampires drain non-sentient beings and/or monsters, and if those beings are drained to death, do they become vampires or vampire spawn, and would doing so satisfy their need to use their drain powers?

Answer 1

Vampires can drain non-sentient beings.

From the vampire stat block / template:

Blood Drain (Ex)
A vampire can suck blood from a living victim with its fangs by making a successful grapple check. If it pins the foe, it drains blood, dealing 1d4 points of Constitution drain each round the pin is maintained. [...]

Energy drain (Su)
Living creatures hit by a vampire’s slam attack (or any other natural weapon the vampire might possess) gain two negative levels. [...]

Any living creature can be energy drained, even if non-sentient/non-sapient. Some creature types explicitly call out whether they're living ("an animal is a living, nonhuman creature [...]"), some implicitly call it out in their rules ("unlike most other living creatures, an [elemental or outsider] does not have a dual nature [...]"), and some would need to be determined from context (e.g., dragons are clearly alive in spite of not explicitly mentioning it).

Some living creatures may be immune to one or the other, e.g., elementals are living but don't have blood, so they would be affected by energy drain but not blood drain.

Only humanoids and monstrous humanoids can become spawn.

Create Spawn (Su)
A humanoid or monstrous humanoid slain by a vampire’s energy drain rises as a vampire spawn 1d4 days after burial.
If the vampire instead drains the victim’s Constitution to 0 or lower, the victim returns as a spawn if it had 4 or less HD and as a vampire if it had 5 or more HD. [...]

Both blood drain and energy drain allow any living creature, but actually raising them as spawn requires requires them to be a humanoid or a monstrous humanoid.

Simply draining would satisfy their hunger.

The text in LM says "undead drains a victim's life force, resulting in negative levels," so as long as the target took negative levels, that would satisfy their inescapable craving; actually turning them into spawn is unnecessary. They do separately have a dietary dependence on blood, but that only requires that the vampire "causes ability drain or damage," which they would be able to satisfy with any living creature.