I'm sure it's all be pre planned considering DLC must have been in development for a long time - so I doubt it would be same dev rivals. I'd think they'd be more then happy to have their characters affiliated with other big characters i.e. Crash and Snake (just an example).
Yeah, they probably had talks with license holders to make sure they approved of all interactions with other characters. I'm sure media molecule was pretty stoked to have Ken Levine write a story for Big Daddy that involved Sackboy.
If Acti had the chance to have Crash grace the same script as a much more renowned character such as Snake or Cloud, they'd be fools to refuse it.