YES

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

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

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