No they will not nessecarily mate, but its likely.
If they really dont like each other, and the tank isnt big enough, the male could quite possibly end up killing the female or vice versa.
I've seen a few cases where a male krib and a female krib were put together that just didnt get along, and eventually the male killed the female.
If the tank is big enough though they might just go on living indefinately without ever pairing up or mating.
But, like i said before, I think that circumstance is far more rare than if they were to just pair up.
-Diana