I don't know about how your organization works, but any one development team with a shared codebase should enforce coding styles. This means indentation but also how common constructs are used. Especially if someone external might work on the code. Some standards are just necessary to achieve uniformly looking code. But some might prevent bugs (For example mandatory curly braces after ifs). It's also just a simple Tool to prevent friction and create a sense of shared code ownership.

External libraries are usually black boxes and you don't work on the code so I don't understand the argument.