I was doing a little dozer work the other day that for a guy that does some logging. There happened to be a couple of gallons of Rotella sitting on my trailer. We were standing around talking and he told me that he uses Rotella for hydraulic/transmission oil in his skidder, loader, tractors, etc. Anybody ever heard of that or have thoughts on it?

Sure, as long as the oil meets the specs it can be used where ever. Key is the specifications. Quite common in AG and construction equipment too.

Not uncommon.

I have a Scag ZTR that uses HDEO (15w-40 or 20w-50) for the hydraulic drive system as well.

On my jd 550h john deere recommends 15w 40 for everything. Final drives, motor, hyd trans, and hydro's. I was kind of surprised myself when I was told this. I swear I asked them 5 or 6 times just to make sure.