DMs at my table say nope all of the time by making it random. Besides, if you get monkeys, they can be commanded to Help the melee PCs. They can be commanded to form a line and all do the Dodge action. Let alone the places that they can get into. Monkeys rule in 5E.Obviously. Milage may vary, and I can see a point being made that some DM's might dislike Raptors or so, but I've yet to see a DM say "nope" to a Druid who wants to summon a pack of wolves. Or "Reef sharks...? You are getting monkeys, my friend".