Do the F-18's leading edge flaps deflect symmetrically in rolls?
Quoting the F/A-18A,B,C,D Flight Manual A1-F18AC-NFM-000, I-2-42


  2.8.2.8 Control Augmentation System (CAS) [...] The lateral control system uses ailerons, differential
  trailing edge flaps, differential leading
  edge flaps, differential stabilator, and rudders to
  achieve the desired roll characteristics. Scheduled
  air data roll rate feedback is used to augment
  inherent airframe roll damping. At high
  airspeeds, aileron travel versus stick movement
  is reduced and the ailerons do not deflect above
  600 knots. Differential stabilator and differential
  trailing edge flap travel is reduced at high speed
  to prevent exceeding structural limits. The leading
  edge flaps deflect differentially up to ± 3°
  when below 30,000 feet and above 0.7 MACH. Differential flaps are not used in the takeoff or land modes nor above 10° AOA in the auto flaps
  up mode. At low airspeeds, aileron and differential
  stabilator travel are reduced with increasing
  AOA to minimize adverse yaw.


In short: Yes the F18 uses differential (asymmetric) deflections on the leading edge flaps and trailing edge flaps but the scheduling depends on angle of attack, airspeed and Mach number.