First, jingles for your boy. Sorry to hear he has slipped. 
Do you know if the clinic is saying they canāt x-ray his hip because they think the results wonāt be readable for diagnostics? In your shoes Iād really want to know what youāre dealing with.
āHip fractureā is such a broad term and the prognosis and healing time are so varied depending on where. Tuber coxae fracture, also sometimes called a āpelvic wing fractureā? You are probably fine going this route. Acetabulum fracture? You are really going to want to get some rads/films of this area because the time and therapies are different.
My horse had a total wipeout years ago and fractured his ribs and his pelvis in three places. He had a wingtip fracture, acetabulum rim fracture, and IIRC, ischium (sp?) fracture. The wingtip fracture had the best prognosis for return to sport and the least heal time; I think it was something like 6-8 weeks. The other fractures were much more severe and guarded. Iām lucky my horse returned to a riding career at all. I started a thread about it if youāre curious. I think it was in 2016.
I remember the day it happened he already had developed a huge hematoma over his hips and the vet did not think his portable x-ray machine was strong enough for a good reading. My horse was in no condition to get on the trailer to haul to a clinic since there was no way he could have pulled himself over the ramp. Once the hematoma subsided I coaxed my vet into taking ultrasounds/x-rays of the area. Initially he was reluctant to do so since he did not think his machine was powerful enough, but we got clear enough rads and films to understand we were dealing with multiple fractures within the pelvis. See if your vet can be convinced: sometimes, they donāt want to waste the clientās money with poor rads/films.
In the meantime keep him in a medical paddock like the vet said. Something the width and length of two stalls max. My horse lived in that paddock for 6 months before we gradually opened it up via pen panels. Movement can make it significantly worse.
Good luck and keep us updated. 