Tinfoiol Barbs get bigger than Oscars, that's why I don't use them. Silver Dollars work great for me (with my Oscars) because they're a lower bio-load and they're super fast. Great cleaner uppers, too. If you're planning on an Oscar, 2 Texas's and a Jaguar in a 180 gal tank it's my opinion you're asking for trouble. 4 territorial Cichlids in a 6' tank just isn't enough room. It'd probably be the Oscar who ended up mortally wounded or dead.
Jags, oscars, and texas rarely need dithers to draw them out into view ... and unless breeding, really don't need target fish. Though the other cichlids would act as targets for the pair.
But if just want schoolers, I'd go with the silver dollars.
I had some neon rosy barbs that hit 5 inches. I didn't use them as dithers, but they would work. Awesome fish! They are active schoolers with exceptional color(males are pinkish-red, females are gold). You're biggest problem is going to be finding large ones that can go straight in your tank. I've also used large rainbows(bosemoni and reds) ar dithers. More then likely, you'll have to grow out your dithers to a suitable size before adding them.