vegetarian BB -- possible but bad results
vegan BB --- totally impossible
Bill Pearl and Andrea Cahling were vegetarians.
You can't be a good bodybuilder and a vegan at the same time.
It ain't easy. But, it can be done. However, your diet would have to be near-letter perfect.
That means knowing the right combinations of vegetables or vegetables and grains that make complete proteins. The biggest hurdle is the consuming those veggies and grains in high volume, especially with fiber suppressing your appetite.
Then, there's the B-12 issue. Unless you munch on organic veggies (which would cost you several appendages), you'd have to use B-12 supplements.
The vegan road is hardly an easy one. But, you can definitely be a good bodybuilder, IF (and I stress, IF) you have your dietary stuff together.