If they are bought as juvies, and getting along, they have a pretty good chance at pairing up, you'll just notice one will grow much faster than the other.
If they fight to where there is alot of fin tearing, only then would I worry/pull one.
You'll most likely be fine.
In a nem dedicated tank, I like to at least add nem safe inverts to mix it up/add flare, so like a nem shrimp, sexy shrimp, or a porcelain crab would be cool, and maybe a cleaner shrimp.