If it has some hrs on it and you don't know when it was changed it would be a good idea. You also should have oil in the final drives (motors that move the tracks) - they mostly don't hold much (maybe 2 qts) and that oil is sealed in there and not part of a bigger system so it should be changed.
As for the Hydro oil, Kubota mostly says UDT oil, but really for it being an older unit I would use any major brand Hydro oil that meets the Kubota spec (Most the big companies say they meet the following specs on the back of the 5 gallon jug and it lists a BUNCH of major manufactures such as Kubota)
May want to change your fuel filter as well (If it gets clogged you won't be doing anything)