How do I get certified to fly under FAA 333?
The FAA's FAQ says:


  Is an FAA-issued pilot certificate required to operate a civil UAS under an experimental airworthiness certificate or a grant of
  exemption under Section 333?  
  
  If the aircraft is issued an
  airworthiness certificate, a pilot certificate is required.5  
  
  Pilot
  certification requirements for petitions for exemption under Section
  333 are evaluated on a case-by-case basis.


The footnote links to this FAA order called Airworthiness Certification of Unmanned Aircraft Systems and Optionally Piloted Aircraft, which says:


  b. UA PIC Certification and Ratings Requirements.  
  
  (1) The PIC must hold and be in possession of, at a minimum, an FAA private pilot
  certificate, with either an airplane, rotorcraft, or powered-lift
  category; with single- or multiengine class ratings, appropriate to
  the type of UA being operated.  
  
  (2) The PIC must have and be in
  possession of a valid second-class (or higher) airman medical
  certificate issued under 14 CFR part 67, Medical Standards and
  Certification.


So, it looks like there are two possibilities:


Your UAS has an airworthiness certificate, therefore you need a pilot's license per the Order (private at least, not sport or recreational)
Your UAS doesn't have an airworthiness certificate, therefore your section 333 petition will be evaluated individually and the FAA will tell you if you need a license or not