Ich hab ne andere erklärung ergoogelt:
Given that the two characters were similar, and they were going to be played by the same actor, some thought *was* given to make the characters the one and the same Nick Locarno. But TPTB felt that Nick Locarno, even with his "code of honor," was too "unredeemable" a character to use--after all, the guy caused the death of a fellow cadet and tried to cover it up. So they decided to keep the two characters distinct and separate despite the similarities and despite being played by the same actor. In fact, Tom Paris' character was deliberately distinguished from Locarno: while both characters were involved in scandals and cover-ups involving the deaths of teammates, in Locarno's case, he instigated the cover-up, while Paris was the guy with the conscience who decided to confess the wrongdoings (like Wesley in "The First Duty").
EDIT: Viele Seiten behaupten aber auch, die Autoren der Folge hätte jedesmal Geld kriegen müssen, wenn Nick Locarno in VOY aufgetaucht wäre.