Show me proof.
You mean the same way Nintendo let's PDP, Hori and others make officially licensed 3rd party products? Nothing new, and Nintendo will always let you if you pay their licensing fees. PDP certainly isn't known for their quality in any shape or form.2. Nintendo has recognized him by allowing an amiibo, which are traditionally made for characters who are featured in Nintendo games, to be made for him.
Every indy developer known to man would be open to the idea of their character being in Smash, it's a no shit situation of free promotion.3. Yacht Club is obviously open to the idea and Nintendo most likely wouldn't have to jump through a bunch of hoops to get him in there.