YES

Problem:
 f(f(a())) -> f(f(f(a())))
 f(f(a())) -> f(a())

Proof:
 Uncurry Processor:
  f2(f(),f2(f(),a())) -> f2(f(),f2(f(),f2(f(),a())))
  f2(f(),f2(f(),a())) -> f2(f(),a())
  Ground Confluence Processor:
   confluent by decision procedure.