Cemetery Reaper grants +1/+1 to all other Zombie creatures you control, not just the ones its ability puts onto the battlefield.

A "creature card" is any card with the type creature, even if it has other types such as artifact, enchantment, or land. Older cards of type summon are also creature cards.

The creature card in a graveyard is exiled as part of the activated ability's effect, not as a cost. If that card has left the graveyard by the time the ability would resolve, the ability doesn't resolve and you don't get a Zombie token.