There is NO industry classification for hydraulic oil. Each manufacturer establishes a minimum requirement for oils to be used in their equipment.
With that being said there are wide variences in available hydraulic fluid. While I personally don't have any experience with Tellus, I've never heard anything bad about it. In the dozen or so different hydraulic apps I have every one use the Deere HyGard/HyGard low vis. Its readily available for me and from what I understand is one of the best fluids available, exceeding their own spec of JDM J20C/J20D.