It is alleged if Covenant had performed its duties to the company and showed due diligence, National Finance would not have made further advances, including a yet-to-be recovered $4.1 million.
If O'Halloran is held liable to National Finance, it argues Covenant should indemnify it, or contribute to any liability.
But Covenant's lawyer Matthew Harris claimed in the High Court at Auckland yesterday that the trustee's duty was to investors, not to National Finance.
Its role was to protect those who had invested money in the company, "not to save the issuer [of securities] from itself", he said.
He applied to have O'Halloran's claims against Covenant struck out.
Associate Judge Roger Bell reserved his decision.
National Finance director Trevor Allan Ludlow, 52, was sentenced in the Auckland District Court last month to six years in prison for his part in a $3.5 million fraud.
He was convicted in July of seven charges brought by the Serious Fraud Office relating to theft as a person in a special relationship and false accounting.