Lets see:
You have Woods, Bradco and Bush Hog that all make hoes to fit. If you buy a large frame tractor as in the "M" series, you shouldn't need a subframe as the frames and cases are substantially heavier than the L series units.
My last tractor, a 5030 HSTC required a subframe for the FEL whereas the M9000 I presently have has no subframe for the loader. That tells me that frame wise, the M's are able to handle the stress of the loader and should be able to handle a 3ph mounted hoe with no problems.
Personally, whatever way I went, I'd get the pto driven pump and holding tank for the hoe. That way, the hoe is completely seperate from the tractor hydraulic system and any problem with the hoe's hydraulic system like a ruptured hose won't drain the tractor's hydraulic system. You can also use a cheaper AW hydraulic fluid in the hoe as opposed to say SUDT that's in the tractor.