Honestly, Nintendo is pretty 3rd party friendly... to some.
They have been uber friendly with a lot of long running major Japanese developers in more then a few ways. They seem to have gotten more friendly with some smaller developers that prove their salt in some games and at times absorb them into the Nintendo fold. But even now, while they aren't as active in the past, Nintendo seems to have good relationships with the likes of Bandai Namco (or Namco Bandai), Sega, Koei Temco (although that might be because Nintendo co-owns Fatal Frame from the looks of things) and even Capcom to a degree.
They are less friendly with so major Western third parties, whether this is because of the language barrier, economics, some long held grudge over previous treatment, the perception of Nintendo being a competitor for sales on the devices or whatever, you see it.
Weirdly enough the two Western publishers you could say Nintendo had the best relationships with until midway through the Wii life cycle or recently were UBI Soft and EA. Time will tell if any future success can ever heal the rift between the companies given how badly things have gotten.