From what I understand Nino's crew was a very powerful street crew and Nino was closer to Delacroce and Big Pauli than other crew leaders because he was a good earner and Pauli was (understandably) afraid Nino and his people. Pauli (alledgely) pretended not to notice Nino's drug-dealing soldiers while he forbidded Gotti's people from doing the same.

I don't think that Nino was in line to be UB in any sense of the word, Thomas Bilotti got the nod after Dellacroce died and Paul was intent on making Tommy Gambino boss after him. Even if he wasn't arrested and died in jail there wasn't much room for advancement for Nino.