So a quick question, I'm assuming for 016 issued tickets if Boutique flights has a delay can you call UA to switch to a UA flight? I'm looking at DFW-ATL (via GLH).
No, you're subject to the rebooking provisions of the contract of carriage of the airline you selected, Botique Air.
While technically correct, there have been numerous reports of UA doing such rebookings. But best not to count on it, but if needed I would give it a try.