To me the fact that you were reading the names of a list online and the fact that it didn't click for him until you brought up that it was his ex-fiances cat's name it doesn't seem like it was intentional. Also I don't know everything but how long ago was the death of the ex? If it was a long time ago it may be a coincidence but if it short amount of time then yea something may be up there. You guys agreed on the name because it fit the personality so it doesn't seem like it was something to spite you or anything. Your feeling in this situation do matter and it's good that you voiced it to him.

He may be uncomfortable with the name because you are and he doesn't want anything that is going to be around the house for a couple years to constantly make you uncomfortable.

Also someone that also is allergic to cats make sure that you take a lot of allegra lol