Edgar Allan Poe is a curious case. In many ways, as the narrator points out, Poe is like Abe in that they both lost their mothers and are both more than a little morbid. (We would add that they both have weird, dark senses of humor in real life, though that doesn't really come up in this book.)
But whereas Abe wants to kill vampires, Poe is kind of entranced by the whole dark brooding thing: "But Poe wasn't interested in learning about vampires to better hunt them—he wanted to know about the experience of living in darkness, of moving beyond death, so that he could better write about it" (4.71). In other words, the dude isn't afraid of vampires, and he doesn't hate them. In fact, sometimes he seems to want to get a little too close for comfort. Take it from us: Poe would be a big fan of Buffy the Vampire Slayer.
But even though Poe is romanced by the dark, brooding, romantic undeadness of vampires, he's not really on their side. That is, he may refer to them as "superior creatures" (4.77), but he also assigns himself the dangerous task of finding out what the vampires are up to so that he might help defeat them. He makes friends with a vampire called Reynolds in order to understand the evil vampire conspiracy—not to be confused with the good vampire conspiracy that Henry belongs to (8.77).
Poe doesn't actually find out what the conspiracy is, but he tells Lincoln everything he knows: about how the vampires came to America to find freedom and safety from European peasants; and about how there's some "great calamity" coming (8.99). As much as he might like the toothy things, he's not about to cheer on a coming calamity, even if he's not sure what it is (Spoiler Alert: it's the Civil War). He may not know everything, but this information man knows enough.