I don't know much about music theory at all. To immediately give my answer to the question in the topic, I say, no, you do not need to know music theory to write, play and perform well on an instrument. I would add that I assume knowing theory would add to your knowledge of music and that can only be a good thing. My own area of theoretical knowledge relates to Literature, and I can approach a text from a variety of angles I'd never have imagined, had I not been trained at university so to do.
I would most likely enjoy and benefit from a greater knowledge of music theory, but I have only so much time left to devote to any hobby/interest, so l'll continue to enjoy my amateur status and see myself as a bass player rather than a musician.