You have to make sure you take their registration paper 'cause some of the info needs to be on the Xray.
Taking OFA X-rays is a bit of an art. You want the dog positioned just so for the best X-ray. If the dog's hips are rolled sideways a fraction, or something else is wrong with the positioning, the hips might not look as nice as they are. This happened to one of my dogs. Make sure your vet knows how to do it right.
Also, some vets will take the X-ray under sedation without putting them all the way asleep. You might ask about that, too.
I have actually gone to a specialist to make sure I got the best Xrays, but I'm sure that, if you trust your vet, they will do a fine job. Doesn't hurt to ask about it, though.