Yes. To get the numerator and denominator of a rational number you have two procedures you can use:
(numerator (/ 6 4)) ⇒ 3
(denominator (/ 6 4)) ⇒ 2
As it demonstrates the values returned are the lowest terms. The report specifies the denominator is always positive and the denominator of 0 is defined to be 1.
There has been no change in this behavior for a long time. I see the same description in R3RS until the latest R7RS so you can expect it to exist in all implementations of Scheme that exists today.
Just for fun:
(define (split number)
(cons (numerator number)
(denominator number)))