Yep, we feed them. I think it's less the salt content (after all meat contains salt as well), than that they are lower in fat than real meat and babies have greater fat needs than we do. I did some research and it seemed to be fine, in moderation, and if you add a little extra fat (like cheese or butter).
My husband eats meat so he cooks it a few times a week and otherwise we eat vegetarian. Our daughter eats what we eat so if it's quorn, I give it to her. Usually not more than once a week and I try to add in extra fat with some grated cheese on top or feed her something along with it that has more fat (like cashew butter or avocado). The sausages are a favourite of her's (and certainly less salt than real sausages).