YES

TRS:

  __(__(X,Y),Z) -> __(X,__(Y,Z))
  __(X,nil()) -> X
  __(nil(),X) -> X
  U11(tt()) -> U12(tt())
  U12(tt()) -> tt()
  isNePal(__(I,__(P,I))) -> U11(tt())

max/plus interpretations on N:

  ___A(x1,x2) = max{0, x1, x2}
  __#_A(x1,x2) = max{0, x1, x2}
  nil_A = 0
  nil#_A = 0
  U11_A(x1) = max{0, x1}
  U11#_A(x1) = max{0, x1}
  tt_A = 0
  tt#_A = 0
  U12_A(x1) = max{0, x1}
  U12#_A(x1) = max{0, x1}
  isNePal_A(x1) = max{0, x1}
  isNePal#_A(x1) = max{0, x1}

precedence:

  __ > nil = U11 > tt = U12 > isNePal