The three gambling companies hoping to win Maryland’s sixth and final casino license in Prince George’s County cleared a critical regulatory hurdle Thursday when the state’s Lottery and Gaming Control Commission declared that all three are qualified to proceed with their proposals.

At a hearing in Baltimore to consider “the integrity, financial stability and responsibility” of the casino operators and their principals, the commissioners voted unanimously to allow the three bids to go forward, but not before concerns were expressed about two of the bidders — Greenwood Racing and MGM Resorts — and their relationships with convicted felons and, in MGM’s case, organized crime influences in Asia.

Greenwood Racing, which is hoping to develop a facility on a vacant lot in Fort Washington, came under scrutiny for chairman Robert Green’s past dealings with Robert Brennan, the former head of penny-stock brokerage First Jersey Securities.

In 2001, Brennan, with whom Green had done business, was sentenced to more than nine years in federal prison for money laundering and bankruptcy fraud. As a condition of qualification in Maryland, the state’s gambling enforcement chief, John Mooney, recommended that Green refrain from making any contact with Brennan.

“I’m agreeable to that,” Green told the commission. He said he had not done business with Brennan since the 1990s and last spoke with him “eight or nine months ago.”

See previous stories in an occasional series exploring the changing casino industry and gambling culture in Maryland.

New Jersey and Massachusetts gambling regulators have placed restrictions on Green’s business dealings with Brennan but not personal contact. There are, he said, no restrictions on his license in Pennsylvania, where Greenwood operates Parx Casino.

MGM, which is hoping to develop a casino resort at National Harbor, was similarly scrutinized by Maryland regulators for its partnership in Macau with Pansy Ho, whose father, Stanley Ho, has been alleged to have ties to organized crime.

MGM was also investigated for its dealings with a former director, Terry Christensen, who was convicted in 2008 on federal wiretapping charges for conspiring with Anthony Pellicano to wiretap the ex-wife of Kirk Kerkorian.

Jim Murren, chairman and chief executive of MGM, said the company “already made that determination” to cut ties with Christensen several years ago. “I’m fully supportive,” he said of the recommendation.

State investigators also studied MGM’s high debt load, Mooney said, but determined that the company “appears to have the financial resources and borrowing capacity” to qualify for a Maryland casino license.

The state’s regulatory enforcement division recommended that MGM officials file periodic status reports on their Macau operation and to refrain from any personal or business contact with Christensen.

Prince George’s Racing Ventures, the Penn National Gaming subsidiary that wants to develop a casino at Rosecroft Raceway, sailed through the hearing.

The background checks presented to the commission took nearly five months, said lottery director Stephen Martino, with 21 investigators — including accountants — putting in 4,500 hours and interviewing 75 people for their suitability reports.

Maryland’s search for its sixth casino site now moves to a location commission, which plans to visit the three sites and hold public hearings on the proposals the week of Oct. 21.