Eh.
A line, drawn somewhere, sure.
Humans being humans, there's a good chance the rules on UBI will expand to exclude more and more people — we already see that with existing benefits systems.
But none of that means we couldn't do it.
Your example is pets. OK, give each pet their own mansion and servants, too. Why not? Hell, make it an entire O'Neill Cylinder each — if you've got full automation, it's no big deal, as (for reasonable assumptions on safety factors etc.) there's enough mass in Venus to make 500 billion O'Neill Cylinder of 8km radius by 32km length. Close to the order-of-magnitude best guess for the total number of individual mammals on Earth.
Web app to play with your size/safety/floor count/material options: https://spacecalcs.com/calcs/oneill-cylinder/
> It just happens that many living beings don't contribute to the goals of whoever is in charge and if they get in the way or cause resource waste nobody will care about them, humans or not.
Sure, yes, this is big part of AI alignment and AI safety: will it lead to humans being akin pets, or to something even less than pets? We don't care about termite mounds when we're building roads. A Vogon Constructor Fleet by any other name will be an equally bitter pill, and Earth is probably slightly easier to begin disassembling than Venus.