You definitely want to run a hydraulic auger tied straight into the tractor hydro. Changing from mechanical torque to hydraulic, back to mechanical torque again taxes efficiency. The same thing happens with a PTO driven 3ph backhoe. A rear PHD operates on a line of direct drive. If you want to operate a hydraulically driven front unit, it's best to tie straight into the tractor hydro than to convert energy from one form to another then back again. You just lose too much of it in the transformation.
That being said, Radman is correct in that you do have to have enough flow. Yours is not a typical CUT, however; it is a commercial tractor and though I do not know for certain, likely has a heavy duty pump that's able to do the job.
As already stated, hydro models can be reversed if stuck, direct drive 3ph models can't. On a 3ph PTO model, you need to lift the auger frequently to clear the spoils. With front hydro models, some people take the FEL bucket off and use an adaptive mount in the center.
One good thing about the front mount PHD is that you can use the FEL arms for downpressure if digging in hardpan. With a 3ph PHD, you'd need to add a downpressure kit for that, or weight the top of the gooseneck with ballast, which is what I did with mine. If you were to do a lot of digging as part of a commercial business, I would recommend using a Pengo auger and having a carbide tip on hand for those times when you have to drill in hardpan.
