1300-1400: Did a quick skim of the Tales (& kat's DB) - can't find any mention of Morris Dancing. According to Brewer's, Morris was introduced in the reign of Eddie III (1327-1377), so it's certainly possible that Chaucer knew of it. However Brewer's also specifically says that MD became popular in the 15thC & later.

Whilst it's absence from the Tales (along with any mention of the wren hunt, as far as I can see) doesn't preclude him mentioning either in other works, I'm now going to change my mind & say false, since my earlier answer seems to have been taken as incorrect!