The wife who sees a lot of specialists never needed referrals until she started using Medicare. They required them. It was a big annoyance for her as she wasn't used to having this extra layer of nonsense involved. The referral also got charged off, so it was more expensive for the insurers than before.
Preventative medicine is over rated, and the VA is very much hit and miss. There are some good facilities and there are really bad ones. The wait times can be anywhere from short to you're going to die before they get to you. Almost all veterans I know see the VA as the medical provider of last resort. I sure do. I wouldn't use them unless I had no other choice. And, I also know the Phoenix VA center is one of the worst in the nation. The Tucson center, by comparison, rates as very good.
I can use any doctor I want on my plan. If I use the ones they have a deal with the whole amount is paid. If I choose otherwise, I just have to make a deal that they'll accept the insurance amount, which they usually do otherwise I foot the difference out-of-pocket. The insurance still pays me the rate they would anyway.