Bettas are not fish eaters by nature. Take a look at that upturned mouth - it is evolved as a powerful mosquito killing tool. It's for grabbing from below, and would make it very hard for a Betta to bite a quick chili. If your Betta is well fed in a tank that size, he won't take a lot of notice of the chilis. I don't think the cat and mouse analogy works - small fish aren't prey animals for Bettas unless the tank is tiny and very poorly thought out.
He may find moulting shrimp impossible to resist though. They don't move fast and look kind of buglike.
The chilis have noticed the betta though. He's a large fish to them, and they are wary of him. I expect it would be the same for any large bodied fish. They'll soon figure that out. I would get floating plants in there ASAP, and expect the Bororas to move lower in the tank and avoid the surface. He'll chase at the outset. It doesn't continue.
No fish occurs in the wild with a long finned Betta - they are human made creatures. But with wild ancestral Bettas, fish like chilis do occupy the shallower habitats. Corys, as South American fish, no (and that gravel isn't ideal, as
@Byron has pointed out).
You may find that when the Corys shoot to the surface to breathe, they will startled the Betta for the first short while.
I feel like a devil's advocate here, but my male fancy Bettas always ignored tankmates like chilis, harlequins or cardinals. They scavenged dead 'floaters', but never bit living tankmates. With those dragging fins, they couldn't catch them if they wanted to. After the shock of seeing another fish (they are raised alone) wears off, they were always very cool here. My sample is probably 30ish individual males over the years.
