The first part is not irrelevant. Say for example the united players call Rooney Shrek out of affection? He might laugh about it in public but he might not like it. He won't say anything though because it might cause aggro.
The second part is plain enough: Ronaldo was ****in' Portugese, Hernandez is Mexican. The expression 'South american term' you quote is the gibberish as there's no such language as 'South American'. Apart from the indigenous languages it has its main origins in Spanish (the language in Uruguay - Suarez, the main language in Mexico - hernandez) and Portugese (the language in Brazil for example) with slight variations perhaps. Spanish and Portugese aren't the same language but they are similar. The word negro is used in the Spanish and the Portugese.
So if the nickname exists, someone of Spanish or Portugese origin in united must have known how to phrase it - possibly Hernandez - not that I'm saying it originated from there but who's to say no one knew about it apart from Evra himself. Hernandez, perhaps. A friend of Evra's in the side. Evra himself even - which wouldn't surprise me. Someone said the nickname was used in one of his own clubs. He might've liked it - HE MIGHT'VE FOUND IT AFFECTIONATE!
Therefore, if Suarez knows about the nickname and knows the united team use it - and I say 'if', since we plebs don't know as we're all being speculative here - and if it is the villain of this saga, then a) the united team should be told off b)Evra hasn't got a leg to stand on.