QWhen playing this follower's ability, do I have to reveal the card from my deck before adding it to my hand?

AYes. This is necessary to show that the card is one of the cards specified.

QIf there are no followers with an evolve ability in my deck, can I still play this follower's ability?

AYes, you can. After looking through your deck, you would shuffle it without adding a follower to your hand.