Separate bookings aren't protected on BA, and there's no reason to think you'll get any indulgence from BA when the operating carrier is Vueling.

You're probably overthinking this anyway. Gatwick is small and efficient, and though there are a few delays showing on BA2204, there's nothing hugely worrying. U2 will leave from the North Terminal in most cases, so you have to grab any checked bags, take the shuttle, drop bags again, and go through probably the best standard security in the UK in terms of efficiency. I wouldn't be worrying at all about this connection at this point,

I might book a cheap flight as a backstop later in the day if there happens to be one available, but I wouldn't be expecting to use it.