being a hellbred is irrelavant. spell focus (evil) has a requirement for the character to be evil, so if he is evil he can take the feat, if he is not he can't.
To expand on parinho's answer, Evil Exception allows a hellbred to cast [Evil] spells and use evil magic items without harm; it doesn't mention feats, and doesn't actually count your alignment as evil in any case, so he wouldn't be able to pick up SF: Evil.