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: 
Yes.
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Unless explicitly forbidden, Merits (like Striking Looks) do apply to Discipline rolls.
Striking Looks explicitly does add to Majesty rolls, as I recall.

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