Kioti isn't going to specify another manufacturers proprietary brand. Kioti does make there own brand of HST fluid.
I have a couple of 5 gallon containers of it in case I ever change the entire 11 gallons at once. So far no need, I only change the filters, by recommendation of my dealer, in over 1,500 hours on my two Kioti's since 2009.
I find the change the entire HST fluid thing over rated and largely unnecessary, so long as one does not allow contaminants into the system, there should be no reason to have to change it out. The filters are micronic, and the system is sealed. As long as one is using their own attachments, keeps their QA, QDs capped and plugged and stores the machine where rain/snow or other water cannot enter the hydraulics, one should be able to maintain system integrity without a lot of effort. If fluid becomes contaminated or milky- a sign of water contamination, then change it out. All I've ever done over the last 9 years is top off the factory fluid with UTF and wet brake additives, from TSC - as long as it meets or exceeds the specs. that the tractor Mfg. calls for.