I have my own version of vampires and thought a lot about them...
So some important general stuff regarding how their diet works! Vampires are undead creatures, turned that way by a supernatural disease. They cannot produce their own life force and hence require it from other creatures. Without it, they can't heal their wounds, use powers as freely, and they will start to lose any form of consciousness as hunger overwhelms them and turns them into ravenous beasts. Such a state of starvation usually takes about a full month of activity without any sort of feeding.
Life force is easily obtained from fresh blood, which is what vampires have evolved to obtain. Blood from the same species a vampire used to be is most effective (ie, an ex-human vampire will benefit most from human blood) as the life force is the most similar to their own. It's easier to use.
Vampires crave body heat and warmth. They'll be instinctually attracted towards it, like a moth to light. They lack any body heat of their own, so a vampire that used to be warm-blooded will be especially susceptible to this
Vampire bodies passively drain magic and life force, though the effect is so small that it can't sustain them or harm anybody. It does make them appear like a "void" of life and magic, since they're constantly pulling it in and consuming it.
Their senses are naturally more attuned to signs of life. Their brain naturally zeros in towards sounds of breathing, heartbeat, the smell of skin or blood, the pattern of footprints, etc, and can more easily ignore other stimuli in favor of it. This gets stronger and stronger the hungrier a vampire is.
Predator instincts! They'll feel compelled to chase, pounce, bite, etc... They're nocturnal ambush predators and can track scents well. In dark areas they'll compulsively walk quietly.
Predator instincts v2. Vampire brain categorizes people as food, and as such the vampire will also experience a shift in thoughts. Depending on the vampire in question this can be very distressing. (Wanting to eat someone so that no one else can steal your meal can do that to people.)
All vampires have at least mild shapeshifting. This is because when they're turned into vampires, their soul fuses with their dead body, forcing it to resurrect. As consequence, a vampire's emotions and self-identity can physically change their appearance.
All vampires also have two types of venom! The first one is the only one that matters for the content I'll make though, so. That one is what's produced and put into the bloodstream when they bite anything. It's an anticoagulant and an anesthetic. It forces the victim to relax and experience an airy druggy feeling, making their mind completely empty and basically incapable of feeling anything but calm pleasure. This venom is also present in a vampire's saliva and stomach lining, though in less concentration.
So when it comes to vore... a vampire could very well swallow a being whole. Whether because they shapeshift to take a form that could do so (bigger size, some new creature, a set of jaws that can accommodate, whatever) or they're already capable of it. Vampire bodies will be geared towards digestion and immediately wanting to consume their prey... but safe vore is definitely possible.
Any vampire hardset on not harming their prey can stop their stomach's digestion. Same idea as their shapeshifting! The emotional intent and self-view of being someone who wouldn't hurt their prey prevents their body from doing so. Instinctually they'll still crave it, but any vampire with enough will can override that.
You can get a vamp with a very grumbly and active tummy because it wants to eat, but the prey is fine because the vamp insists on keeping them safe.
