O'Leary and Gardner are due to go to trial at the end of this month. The SFO alleges the men used a large portion of investors' money to fund their own personal interest in Gisborne Haulage and Michael Ward, 1969, which operated Jean Jones womenswear label throughout New Zealand.
Justice France said while Simpson's actions had cause harm to a lot of people, he was not one of the principal offenders in the case.
"Their money was invested because they trusted in you and you abused that.
"Rockforte Finance was seen as a local business run by local people that could be relied upon," he said.
Simpson, who had been a bank manager in Gisborne for more than 20 years, had owned up to his offending and volunteered to help in investigations against O'Leary and Gardner.
Justice France said the father-of-three had also remained involved in the Gisborne community since Rockforte's demise, and had taken up three low-paid jobs to support his family.
A sentence of community work and home detention reflected Simpson's remorse and assistance in the Crown case against his co-accused. It would also enable him to contribute to the community, Justice France said.