Fortunato may not really believe that Montresor is playing a joke on him when he chains him to the rock wall and begins to wall him in. Montresor says that Fortunato is a man to be respected and even feared. In desperation, Fortunato may be trying to implant some doubt in Montresor's mind and at the same time may be giving him an excuse to relent and release him. Fortunato says that this entrapment is an excellent jest but asks if they shouldn't be going because Lady Fortunato and his guests are expecting them. If Montresor thought that Fortunato would be missed that very night, he might be afraid of a search party tracking Fortunato to his (Montresor's) palazzo or at least establishing that Fortunato was with Montresor when last seen. Fortunato wants Montresor to believe that people in the crowded streets have recognized them both and assumed they were both headed for Fortunato's palazzo, where a big party was in progress. But Montresor had taken the precaution of establishing that Fortunato had no "engagement," was not expected anywhere, when he first encountered him.So Fortunato's ploy does not succeed. However, Fortunato shows that he is sober, that he is clever, and that he is a man to be respected and even feared. If he ever got out of those chains he would show Montresor that he knew it was no jest but attempted murder. He might report Montresor to the authorities, but more likely he would have taken his private vengeance by having Montresor killed.
Quite simply--no, Fortunato does not understand why Montresor hates him. In fact, he does not even realize that Montresor dislikes him or intends to harm him. If he had known Montresor's true feelings, he would most likely have never accompanied Montresor into a secluded area. Similarly, when the effects of Fortunato's intoxication have worn off, he still believes that Montresor's encasing him in the wall is a joke. Even when Fortunato is able to utter his last words,
“For the love of God, Montresor!”
Poe implies that Fortunato is begging Montresor to end the prank. His words do not indicate that he has realized Montresor's true feelings for him or understands the motivation behind the narrator's actions.