Question: When making a roll on Majesty to Awe people, is a Vampire permitted to make use of the +2 (or +4) social bonus for the merit of being exceptionally attractive?

Answer: 
I've gone with the rule of thumb that effects can be stacked unless the rules explicitly say they don't. I don't see anything in the rules saying they don't. Logically it makes sense that beauty would play a role in successfully Awing someone. If I were running the game, I'd allow it.
Striking Looks explicitly does add to Majesty rolls, as I recall.

It's also a +1/+2 bonus, not a +2/+4.