But a Bristlenose (or any bottom dweller) with something that spawns on the substrate, or is always close to the bottom of the tank (ie, Shelldwellers) don't fare well. Bettas and BN would be nice, because Bettas take up the upper half, BN the lower half. But Shelldwellers take up residence in shells obviously on the bottom of the tank. BNs also occupy the bottom of the tank, and from what I've seen, the BNs and SHellies will usually be fighitng for the same bit of bottom-retail.
And for things that spawn on the substrate, like Rams mostly do, in many cases the BN will eat the eggs, and a small fish like a Ram has a harder time getting a Bristnose to stay away, than say, an Oscar would.