I think it's a preferrence thing. I've seen guys that will use only OEM oil in their machines, and I'm ok with that. On the other hand, there are other quality oils out there that are suitable. After all, there's nothing unusual about the Bobcat hydraulic system, they use the same type of hyd components that are used thoughout the hyd world. IMHO, a good quality AW hyd oil will work fine. I prefer AW oil as opposed to RO hyd oil. RO oil has additives to inhibit formation of Rust and Oxidation. AW has these additives as well but also has Anti Wear additives, and doesn't cost much more. The debate is usually which grade to use, 32, 46, or 64. I'm going to climb out on the debate limb and say AW32. Some will say you need 46 or 64 to deal with heat, but the Bobcat has a pretty good oil cooler to control heat, so I think the AW32 will work just fine along with the oil cooler and give good cold weather performance.
My 2