Can you raise your character's main ("Hard Cap" - Level 81) level higher in Dawnguard?

Solution 1:

The answer is no. You cannot raise your level cap beyond the current hard cap which is reached when you max out all base skills to 100.

While Dawnguard introduces 2 new skill trees, Vampire and Werewolf building these trees is self contained and does not contribute to your overall level. You gain perks within these trees through in game actions/achievements, not 'xp'.

Solution 2:

With Patch 1.9, individual skills can be made "Legendary", denoting them with an Imperial symbol. This will reset the skill to 15, and perks used for that skill may be redistributed. Gaining levels in that skill will affect leveling again, thus effectively removing the level cap of 81. There is no restriction on the number of times that skills can be made Legendary. This change makes it theoretically possible to obtain every single perk in the game.

^{Source: UESP wiki, "Skyrim - Leveling" article
(Shamelessly copied from my other answer here.)}

Solution 3:

You may only raise the main player level beyond 81 by using the console on PC version. You are using the PS3, thus you are unable to level beyond the main player level of 81.