No, they aren't vampires because like I said, they weren't dead. In order for it to be a vampire, it must not be a living human.
While vampires can be born (if it is the offspring of say two vampires), they are not born as living humans, but as a vampire.
Other than that physically obvious reason as to why the monsters of
I am Legend are not vampires, another would be that vampires have an actual need for blood beyond the basic "I need to eat" need. Just like psychic vampires, mythical (blood) vampires have a drive that causes them to need blood, and to feel weak, and will lose strength when they are not able to drink. Doing so causes the vampire to age, quickly, reaching its real age usually within weeks, causing the vampire to die.
As well as the fact that in the movie, humans can become this monster by contact, or from being exposed to the air around them. But, unlike the monsters of the movie, one needs to bitten in order to contract the vampire..."sickness" I suppose.
Which brings me to my next point. Vampires aren't made vampires by any sort of virus or radiation or anything in the air. One must be born with the "sickness", or must be bitten in order to be a vampire. Seeing as how vampires are all satanists, and are in fact the negative image of Christ, taking blood to sustain (better their) life, rather than giving blood to better life, there really isn't a way to spread it as an infection.
As well as vampires are immune to modern day weapons, such as a gun or an ordinary knife. These will, at best, be a short distraction for the vampire as his ability to heal almost instantaneously will render him near impossible to actually harm to tire. True vampires can only be harmed by absolute pure silver, or a weapon that has been hand crafted, or wood, specifically to destroy vampires. Yet we see plenty of protection provided by things like guns , bombs, and grenades in the movie.
Even though they may be sensitive to light, that doesn't mean that they are vampires.
By that logic all albinos and gingers are vampires.
So, now that we know that these aren't vampires that were dealing with, lets tackle this zombie business.
First of all in order to be a zombie, the monster in question must have died previously. That is because the infection only works to regenerate the body, and cause it to need flesh in order to...not live or anything, zombies just want flesh.
So, whether it is a corpse that has been put in the ground recently and has been affected by the infection, or the bite of another zombie caused the victim to die a slow, painful death only to be reanimated less than 24 hours later, one must die beforehand in order to be a zombie. Which, would be a quick flaw in why they aren't zombies either.
Another immediately obvious problem with the zombie theory here, is that zombies have no super-human strength, and lack the ability to climb anything. In the movie, we seem jumping around on light poles and scaling buildings like monkeys. This is simply impossible for a zombie to do, as there's no way for it's brain to comprehend the advanced techniques necessary. Let alone the zombie's decaying flesh making it impossible to hold onto anything, or even get a tight grip on anything - other than rigor mortis.
So, while they may appear similar to a zombie in some instances, they lack any of the technical meat to be considered as a zombie.
And finally, "Well, what are they then?"
These things are simply monsters created by the author or the book, and the writers and directors and such or the various movies. They merely are a combination of some of the best (or worst...) qualities present in all kinds of mythical monsters. Such as the sensitivity to light, and super-human strength of a vampire, and the (somewhat) appearance and need for flesh (not just blood - the seen where Will Smith goes into the room full of money in search for Sam, revealing a hoard of them munching away at a body) present in zombies.
Umm, all in all, I think that this was mainly a pretty useless post. But, I enjoy arguing, and I'm fascinated with the various monsters of horror, particularly zombies, so I'll post this anyway.
And If you still think they're vampires, I'll be happy to throw more evidence at you...
