I think you mean coaches.
No, I don't know what is the best word to describe Roig in connection to Rafa, uncle Toni is his coach, Costa is his agent, that's clear. There's a group of other guys that support Rafa in his box during matches and Roig is one of them. According to Wiki he works as the "alternate coach"
He was a good doubles player (even played with Rafa on tour) so maybe he was working partly on Nadal's volley improvement, don't know the details, I don't follow off court relations.