QWhen playing this spell, if I can't select an enemy follower on the field, can I still select a Shadow Paladin follower in my cemetery and add it to my hand?

ANo. If you can't select an enemy follower, you can't play this spell. However, if you can select an enemy follower but do not have a Shadow Paladin follower in your cemetery, you can still play this spell. That's because "select up to 1" means you can select 0.