Another important question might be how many know what vampires really are?
I like to think that the Calabim may have spread a few rumors, at least among their own serfs, approximating more common vampire lore of our world. (I remember that in one D&D campaign Kael enjoyed letting an adventurer spend most of his funds on garlic and maybe holy water before facing a vampire lord, and that said player was rather upset to find that such things have no effect. Calabim vampires might enjoy spreading rumors of such weaknesses and then showing those who defy them how wrong they were.) Commoners may believe that they are going to loose their blood, but it is likely a much more closely guarded secret that vampires actually devour souls.
Calabim commoners are in general the worst educated people in Erebus. I doubt many ever learn to read, and they likely lack even oral tradition because no one makes it to become an elder. Thus, they may know less than would be expected of their lords' true nature. They do however recognize dull yellow eyes, a pale complexion, and a perpetual sneer as marks of nobility.
I vaguely recall reading (in something not-FfH related but which Kael may have drawn upon) that the term Moroi is sometimes used to refer to the children born to a vampire. This makes me think that many Moroi may be drawn not from the chattel class, but from the biological children of vampire aristocrats. This may give them some degree of distinction similar to lower nobility or gentry in other societies, but in order to become full fledged aristocrats themselves they would have to first prove themselves worthy of being given the gift (that is taught how to murder a man in such a way as to drain all the energy from his soul). Flauros likes to consider the Calabim a meritocracy, because all of their noble had to earn their rank personally rather than inheriting it. In human society many weaklings gain wealth and power purely by being born "rightful heirs," but the concept of heirs does not exist when those who have anything worth inheriting firmly believe they will never die.
(Interestingly enough, it seems more traditional Eastern European uses of the term Moroi referred to a type of vampire which, like the Calabim, did not subsist on blood but energy drained from mortal victims.)
Non vampires (mostly Moroi class I'd guess) frequently serve in important positions such as generals in the Calabim army. They can be very influential (in Decius's case he was even given charge over many old and powerful vampire), but would not be recognized as true aristocrats. The true aristocrats are mostly too busy living lives of leisure to continue with the responsibilities they had as Moroi.