To be fair, I haven't seen a UPS not have surge protection. Yes, they're two separate circuits, but surge protection is typically included.
For that matter, and the discussion at hand, a surge protector is probably all most people will ever need. But I wouldn't use one in because it 'improves audio quality', but because it offers some protection against the heavy thunderstorms we get here.
Yes, but the surge protection in a UPS is fairly rudimentary, and frankly, in the wrong place to be very effective. Good surge protection, particularly of common-mode surges, needs to have a really low impedance ground, and that's not something typically found at the location of a UPS, at least a smallish one in a home or office. There are several classes of surge protectors too. In areas prone to high voltage surges, like Florida, the lightning capital of the world, you need to get fairly serious about surge protection, at the premise level, and a good low resistance ground. At devices, you'll want something that really does protect a surge, that actually senses the overvoltage and disconnect the device, not just a sacrificial MOV.
None of that equates to the surge protection in a UPS.
None of that improves audio or video performance either, unless you consider working gear as out performing smoking gear.
And none of the above is "power conditioning".
I kinda hate the hype-ish presentation but the demo is pretty good:
https://youtu.be/4j8cH6l2YjE
I don't work for the company, and often actually recommend a competitor, but it shows the difference between the hardware store sacrificial MOV surge protector, and something with overvoltage sensing. It doesn't demonstrate a common-mode surge, of course, but you get the idea.