A horse with a hip impairment is a horse with a hip higher than the other one.
Usually it is not annoying on a short term if you don't expect to do competition with him. You can try to make him work to counterbalance the discomfort but it will probably degenerate in time with back problems, ostheoarthritis or even difficulties just to turn (making corners for example).
Yo can help him with using anti-inflammatory but i will strongly recommend to see a vet and make X-ray and see if he has a problem. If he does, don't hesitate to make him see an osteopath but you have to know that it won't last long until he's suffering from it and you can't ride him anymore.