In my (limited) experience, Rainbow Sharks are very calm if they have a cave or two to hide in. As long as no other fish competes for it's spot, it won't bother them either. I've even kept them with guppies and tetras, and they were never bothered. So as long as you have 2 caves that are well-separated (at least 3-4 feet apart), and both sharks are introduced at once, it could work out.
I'm not sure if OP means Rainbow or Red Tailed, though. Rainbow has the red fins, and albino rainbows are more common, so that's what I'm assuming.