I think vegetarian diets can help some people and not do much for others. It certainly isn't a cure.
I was a vegetarian from the time I was 16 on (diagnosed officially at 23). I used to be a lacto-ovo vegetarian for about 9 years. I had symptoms start showing up slowly around a similar time, so even for the longest time my mom thought that my symptoms were DUE to my vegetarian diet. Haha. This year, I have started to "need" something else -- I felt awfully tired and just felt like it was diet related, even though I've never previously had issues with the veggie diet. I brought it up with my rheumatologist and said I had been considering trying fish again...I felt like I was getting cravings. He encouraged me to eat and enjoy basically ANY seafood because they are packed with great nutrients and have anti-inflammatory qualities. He discouraged me from venturing outside the seafood realm (beef, chicken, pork, etc.) because he said all other types of meat have inflammatory qualities. He said I might not notice anything from them, but when you've got on-going issues with inflammation...it helps some people to try and avoid things that could aggravate that.
I've been getting more cravings for red meat this year, but I don't test anemic or anything like that so I continue to avoid it. I do eat fish on occasion (probably only once or twice a month at the most). I mostly can tell when I "need" to add some fish to my diet...then I'll eat it and not "need" it for several weeks again. Outside of that, I continue to have a primarily vegetarian diet.
I think one of the things people have to remember is that vegetarian diets can be really easy to screw up. I know a lot of vegetarians who basically don't eat a ton of vegetables/fruits, but eat a TON of carbohydrates like pasta or crackers. Obviously I eat pasta and crackers too, but I eat a lot of fresh vegetables, eggs, nuts, beans, and dairy. I do struggle with getting enough calories all the time and I have sometimes considered adding meat just so I could bump up my caloric content....but again, both my rheumy and nutritionist discouraged me from adding anything except fish, so I continue to follow their suggestions for the time being!