YES

   1: +(x1,0()) -> x1
   2: +(s(x1),x2) -> s(+(x1,x2))
   3: +(x1,x2) -> +(x2,x1)

@Jouannaud and Kirchner's criterion
--- R
   1: +(x1,0()) -> x1
   2: +(s(x1),x2) -> s(+(x1,x2))
   3: +(x1,x2) -> +(x2,x1)

--- S
   1: +(x1,0()) -> x1
   2: +(s(x1),x2) -> s(+(x1,x2))
   3: +(x1,x2) -> +(x2,x1)