No problem hitching or unhitching on an angle. As mentioned above, having the height of the 5th wheel is important as to not put any stress on the landing gear. The other thing I like to do is back about 2 foot farther then I need and pull forward 2 feet to take the sideward stain of the tires and axles. Being 40 foot long and 3 axles there's not many times I get to be straight on.
Dennis