Why did Roth hire a Sicilian? With Roth being Jewish wouldnt it be a little more smarter to hire a Jew instead of a Sicilian some one you can trust?

My guess is that having Ola gives Roth a cloak of credibility. Ola certainly provides Roth a bridge between he and the predominantly Sicilian Dons he works with. Notice how Ola reiterates Roth's good reputation - "Hyman Roth always makes money for his partners."

Good Point.

This was a real-life parallel to Meyer Lansky, the gangster that Roth was based on:
Lansky had a Sicilian pal--Vincent (Jimmy Blue Eyes) Alo--who was a partner in many of Lansky's gambling ventures. Lansky's credentials with the Mafia Commission were impeccable: he was trusted by all, starting with Lucky Luciano, and including Frank Costello and Albert Anastasia. Vincent Alo helped him negotiate with Italian gangsters at the operating levels with whom he had to deal in Broward County, FL, Saratoga Springs NY and elsewhere.
One other point: "Johnny Ola" is an anagram--"Ola" = "Alo."

Good obsevation about Jimmy Blue Eyes (true story I once met him). Roth only used Johnny Ola for certain things, and he was not respected that much. Frank Pentangeli refers to him as Roth's "Sicialian messenger boy."