I shouldn't imagine it would be a problem as long as you could show you would accomodate a child's needs particularly early on in placement. For example, our therapist has said food is not a battle that is worth the fight early on for our two, and so we fed them fish fingers and chips for dinner every night because we had bigger fish to (ahem) fry. The youngest shouted "dinners ready" every time the airfryer beeped....
Tbh, I doubt many children are only eating steak tartare as their preferred choice of safe food, it is more likely to be crisps, pasta, chips, nuggets etc, all of which I assume you could or would accomodate within reason. I suspect there would be plenty of alternative veggie options, and it sounds like you can be flexible in how this is delivered, so if they really need chicken nuggets or whatever, you can do that.
You might want to give a nod to any thoughts of cultural dishes and accessing or normalising those if you are considering adopting transracially, or how you will prepare your child to eat out with friends to avoid social circle thinning as they get older (the cult of Friday chicken and chips looms large in our area, its a big deal) just so that you can show the depth of your consideration about the impact it may have on them.
Our social worker was a vegetarian and would have been delighted to meet another vegetarian I think! Alas, we did not fit the bill, but she was enthusiastic when we said we did meat free Mondays.
You might also find that foster carers are veggie or vegan anyway- one of our sons came from a plant based household anyway, so we had to gently introduce meat and dairy. I guess it can go both ways!
Good luck with your application!