A: This is a 20-year old garden tractor; and
B: Case-IH AkcelA Ultra Hy-Tran has been, and is, the premier hydraulic/transmission oil on the market. It has the highest water tolerance of any hydraulic oil sold, has the highest filtration efficiency to prevent clogging and cavitation, has the best wear protection of any oil sold, has the best friction stabilization additives to allow smooth operation, and is the standard by which all other hydraulic oils are compared.
Considering that Cub Cadet was owned by IH, and they are the developers of the hydrostatic drive, as well as talking with several Cub Cadet certified mechanics, I'm satisfied that the Hy-Trans fluid will work just fine.