I just had my barium xray last week. However, I have a colostomy, so some of my info might not apply.
I also was NOT told about any prep prior to the xray. However, I chose on my own to do the liquid diet for 24 hours before the procedure. I did not take any kind of laxatives or other bowel prep chemicals. I just did the broth/jello/popsicles/gatorade thing for a day.
I found my xray nurses to be uneducated regarding ostomies as well. I had to show them how to remove and replace the bag. They asked many questions about ostomies - how they work, how they feel, etc. They seemed very curious, which is fine but at the same time a bit unnerving.
While on the exam table, my ostomy started working and stuff came out. So apparently the liquid diet was pointless. But still the xray went fine and they were able to see everything they needed to see. So I guess bowel prep isn't needed .
Good luck.