There's a lot more to health than nutrition
- Stress management
- Genetic / Epigenetic considerations
Regarding DHA deficiencies, it isn't a foregone conclusion that vegans or vegetarians in general will be deficient - perhaps not optimal
In spite of being a vegetarian Paleo, I firmly believe that eating well-sourced animal products will maximize your chances for health. But YMMV! Do what works for you based on the scientific evidence you have before you and validate your n=1 experience FTW!
EDIT - to answer your question, yes it is "possible", but if health rather than ethical considerations is your objective, it does not seem "probable"