So let's say he found a whore and agreed to fuck her for money. Who doesn't, but why doesn't he protect himself? No matter how many times you explain to people the dangers of unprotected sex with a casual partner, they go at it again! Personally I always have condoms with me, women often have them too if they like sex!
The father clearly raised his daughter - Dad is the main thing. You could always find support and encouragement from him. And to suck his cock is just a thank-you for having him. By pulling her on his cock, her father showed how much he trusts her and that secret will be with them now. And the chick did a great job - and daddy is happy and she's even closer to him now.