Blackbeard's Devil Fruit is a unique Logia. You see, he cannot turn into Darkness, whereas for example Ace can turn into fire. Of course Blackbeard can create Darkness and manipulate it.
Yountoryuu: It's like a mixed Logia/Paramecia. He can takes the hits, but gets stronger of it -i believe-
Let me ask something more: I know that Luffy doesn't completely control his Haki yet but is there any possibility for Luffy to manipulated Haki for hiting Blackbeard?
No, the reason is Blackbeard`s DF, it is a Logia but a unique. He can recive hits and the user of the fruit is still vulnerable to attacks as they cannot turn into darkness in order to dodge them. If they fail to absorb the enemy's attack in time, the user can be hurt like any other normal human being or even more, as stated by Teach.
AcheronStyx: his power is also somewhat like controlling gravity (since Moria controls shadows) and due to that power he can be hit, cause if "turned into" gravity you would have to be hit
Liljfuzz: In episode 325 " Blackbeard, Darkness attacks Ace". Blackbeard explains why he can get hit, and he also mentions that he takes more pain then usually does when he gets attacked.