YES

(format LCTRS :logic QF_LIA)
(fun fib 1 :sort (Int Int))

(rule (fib x_0) (+ (fib (- x_0 1)) (fib (- x_0 2))) :guard (>= (- x_0 2) 0) :vars ((x_0 Int)))
(rule (fib 1) 1)
(rule (fib x_1) 0 :guard (<= x_1 0) :vars ((x_1 Int)))

Confluent by Parallel Closedness with proof:
no critical pairs

Elapsed Time:   7.73 ms