For me, it was better not to be there because Dex is very much a mommas boy and wont listen to anyone else when I'm around. He's also a big baby and wants to hide between my legs. If you want OFA then tell them that's what you want. I didnt because it was more expensive and I didnt need it. I was doing the X-rays just for my own peace of mind. I got the results right away even though Dex was still in the back room.
IMO do what your comfortable with, that way you have no regrets.
it's your dog so if you want OFA they will understand.