No its not that simple. I dont know much about your tractor but you will need to remove the valve on the splitter and hook the ram directly up to another valve on the tractor.
Why do you want to use the splitter from the tractor seat?
For a 5in log splitter ram you need close to 16+gpm to get any type of decent cycling time out of the ram. Just looked up the specs for a JD 850, its only got a 5gal hyd capacity so i would assume its prob about a 5gpm pump. Thats going to be painfully slow.
Used lawnmowers are very cheap and with the addition of a few more parts and pieces can be made to run a decent size log splitter with a good cycle time...it can also keep the hours off your expensive tractor.