The simple answer is Yes, if done correctly.
So then the question becomes, what is the definition of correctly.
By Correctly I mean, a person is abstainstaining from eating the flesh of an animal and adheres to only ingesting unprocessed grains, fruits, and vegetables.
You can still be a vegetarian and be unhealthy or obese. If you're eating garbage you're getting garbage in return. Eating processed unhealthy foods is like trying to fuel a jet engine with gasoline, it just doesn't work very well. Even with the vegan diet, one can find a way to still ingest unhealthy foods. Many companies make them. Too much fat is too much and the same goes for sugar.
Personally I recommend the Paleo diet, but if you have no issues with wheats or grains and have issues with meat, I don't see why switching one for the other would make any difference as long as you have no intolerances.