When he first heard of Hans, Kristoff questioned Anna's judgment for agreeing to marry a man she just met. However, since he had never personally met Hans, he had no actual opinion of Hans though he did seem to find it suspicious that Hans would propose to Anna so quickly, questioning his character and how he viewed Anna. Nonetheless, Kristoff understood Anna's feelings for him and for this reason could not understand (or possibly did not want to confront) his feelings for her so she could be happy with Hans. Later on, Kristoff brought Anna back to Hans so that he could cure her frozen heart, not knowing about Hans' true nature. This broke his heart, but he believed Anna would be happier with Hans than with him. He appears to be aware of his betrayal because when Elsa had finished thawing the kingdom, Kristoff was about to confront Hans but Anna stopped him so she could do it herself (resulting in her punching him off the ship).
Although the two have no actual interaction with each other during the film, (other than Kristoff nearly punching Hans after Arendelle is thawed), it is evident that Kristoff is aware of Hans' betrayal and attempt to kill both sisters and hates Hans, especially after he hurt and betrayed Anna, though Hans' view of Kristoff is unknown.