Drewniak is pictured in the video report standing by Iacullo while the lawyer answered questions.
ABC published the report on its website Friday evening. Iacullo could not be reached for comment Friday. Drewniak did not respond to a request for comment.
Grand jury proceedings are secret. A spokeswoman for the U.S. Attorney's Office in Newark would not comment on the report of Drewniak's appearance before the panel Friday or the status of the office's investigation.
ABC also reported that New Jersey's acting attorney general, John Hoffman, had selected a team to continue the investigation if federal prosecutors turn over the case to the state. A spokesman for the Attorney General's Office had no comment Friday.
Drewniak is the first person reported to have appeared before a grand jury in the federal probe into the lane closures, which snarled traffic in Fort Lee over four days in September.
An internal review commissioned by Christie released last week found the governor did not know of the closures beforehand and played no role in the decision to close the lanes.
The report laid blame for the decision on former Christie aide Bridget Kelly and former Port Authority of New York and New Jersey official David Wildstein. It didn't determine a motive, but said the mayor of Fort Lee - a Democrat who didn't endorse Christie's reelection - did appear to be the target.
Drewniak was notified of reporters' questions about the lane closures by Wildstein while they were underway in September, according to e-mails subpoenaed by state lawmakers and cited in the inquiry by a law firm commissioned by Christie.
Throughout the fall, Drewniak remained in communication about the issue with Wildstein and issued statements to reporters that said the lane closures were part of a Port Authority traffic study, and that the governor was not involved in the matter.
Drewniak, like other members of Christie's staff, believed the closures were part of a study and was not aware of an ulterior motive, according to the law firm's report.
According to the report, Wildstein told Drewniak in December he mentioned the lane closures to Christie at a public event while the closures were in effect. Christie has said any mention of a traffic issue would not be memorable.
The investigating law firm did not interview Wildstein or Kelly, who, along with former Christie campaign manager Bill Stepien, have invoked their Fifth Amendment rights against self-incrimination in response to a state legislative probe.
Kelly and Stepien have said they had been contacted by federal investigators. On Friday, Stepien's lawyer, Kevin Marino, said his client had not been served with a federal subpoena.
Prosecutors have subpoenaed documents from Christie's office, according to Christie, as well as from the governor's reelection campaign, according to its lawyer.
A spokesman for Christie's office did not respond to a request for comment Friday on the grand jury proceedings.