Culver's fry oil is listed on their own menu data as canola oil and the brioche bun every ButterBurger is served on lists a seed oil, while 152 of their 246 food components carry an additive including every custard base we read.
Culver's publishes ingredient statements for its whole menu through its own ingredient search. Of 246 food components, 119 contain a named seed oil and 152 contain an additive from our watchlist. Their fry oil appears in the menu data as a component literally named Canola Oil, the Crinkle Cut Fries carry a seed oil, and the Brioche Bun that every ButterBurger is served on lists one too, so there is no standard hot order that avoids it. The frozen custard is the other problem: every flavor base we read - Butter Pecan, Cheesecake, Chocolate and Vanilla, Chocolate Root Beer - carried an additive. The beef being fresh and cooked to order is real and worth something, but it arrives on a bun that undoes it.