Let's see:
Chimchar's egg groups are Field and Human-like. So, it can breed with any B/W (2) Pokemon of the same egg group. No need for both the groups to match.
Charmander's egg groups are Dragon and Monster. So, it can breed with any B/W (2) Pokemon of the same egg group. No need for both the groups to match.
Note: The Pokemon hatched from the egg will of the same species as the female Pokemon.