Knarr
If I pay for a land only with recruit tokens and the Viking deck is empty, can I still draw its free Viking?
Yes, but the empty-deck rule applies first. Nothing was discarded to pay, so if the deck and discard pile are both empty, the player or players with the most Vikings discard one, which becomes the deck, and then you draw it. That can be your own card coming straight back, so paying with Vikings instead is usually better.