Not sure to be honest, but you can have tofu. Quorn is a bit higher in carbs I think.
I doubt a small portion would hurt but of course nothing with breading or batter on it. I am vegetarian and have to tweak Atkins to suit my needs. I don't much care for Tufu unless it comes in the form of ready-made burgers etc from the health food shop! Again carbs can be high in processed foods so reading the labels is essential.
I stuck to eggs, cream cheese and cheddar cheeses as protein sources during Induction. Atkins shakes and meal bars helped add variety as well as extra carb controlled nutrition.
For vegan Atkins advice it might be best to check the Atkins Community site. There is a new Atkins book coming out soon. Foods have been added to it to simplify the various programmes. There is an existing vegetarian Atkins approach. I 'do my own' but site information might help you greatly.