Just because someone has done it and hasn't ripped the steering box from the frame doesn't mean it won't happen
And just because fluid is shared between the two does not mean they work together.
The valve in the steering box will be supplying full pressure/flow to the ram when its cranked all the way, if the draglink wasn't there it wouldn't bind. The ram would be all the way one way and the pitman arm would be all the way one way.
Add in the draglink, which is a mechanical connection between a fixed reference (the frame/steering box) and a moving object (the axle), and things bind.
The hydraulic ram doesn't care what the frame or axle are doing, when you turn the wheel left the valve routes fluid to the ram and it puts pressure on the axle to turn left.
The mechanical setup isn't that way (and it is a hydraulically assisted mechanical setup). You can have the steering wheel turned all the way but the tires aren't necessarily doing the same thing.
This is why it binds.
Again, I'm sure people have tried this and not seen bad effects (yet anyway) and that's because the springs and spring bushings have some give. Eventually it will catch up, the shorter the draglink is the more it clashes with a hydraulic ram.
