They can be, but IME most are model community citizens. Don't attempt to mix your betta with other fish without a back up plan, however.
Glofish and zebra danios need a much larger tank than 10 gallons, as do most cories.
You could do a school of about 6 small fish like neon tetras or ember tetras. Pygmy cories like habrosus would work, but avoid larger cories. I have a school of dadio's with a betta in a 10 gal and that works nice, but those can be hard to find.
Personally, I do think kuhli loaches work in a 10 gal if you have a sandy substrate, but something with a slightly larger footprint like a 15 or 20 would be better. They need to be stocked in groups of 5. A few platties will work in a 10 also.
Bettas usually eat shrimp IME, especially the males, but you could try some cheap ghost shrimp if you'd like. 1-2 nerite snails would be a nice addition.