according to the tellings over mythology, Вампиры have been known to obtain blood by biting a human body and 'sucking' blood for their nourishment. therefore, Ты are correct.
but...if Ты want to get into our interesting century, there are two sides; whether Ты are appealed to Вампиры или not. so therefore, Ты can say that they do "suck" as using the term they "disappeal" to you, but in either way based on our technological terms and based on mythology, we can say that they "suck" no matter what.
...believe me, i don't speak like this always. ^^ '
The term suck is relevant. I believe Вампиры bite into a person's neck and suck their blood. But as for the other definition of 'suck' as in "they aren't cool" или whatever, it depends on the person's interest and therefore, is an opinion.