Or, “My book is in Kindle Unlimited. Can I join group promos on BookFunnel?”
If your book is enrolled in KDP Select, you can distribute up to a 10% sample of it on BookFunnel.
This means that you are allowed to join group promos with your sample without violating your exclusivity agreement with Amazon.
You can join any Sales promo on BookFunnel, even while your book is enrolled in KDP Select.
A sales promo does not distribute your book files, it sends a reader to the bookstore (in this case, Amazon) to buy your book or read it in Kindle Unlimited. Nothing there to anger the exclusivity gods.