No, if you're uncomfortable with "nigga" in the servers, feel free to warn.
I said I personally don't warn for something like that when it's clear there's no discourse between the two people because the whole point of being staff in a server (in my opinion) is to make sure everyone is having a good time. If there's immature dialogue but it's all in good fun, I tend to not ruin the atmosphere. That being said, I won't let racism run rampant, and there is a difference for most people between the hard R and nigga, but it's not the end of the world if you feel necessary to enforce them the same way.