By Sam Youngman

DENVER (Reuters) - Republican vice presidential candidate Paul Ryan will meet behind closed doors with donors and fundraisers in Las Vegas at the Venetian hotel, owned by casino mogul and formidable campaign donor Sheldon Adelson.

The Wisconsin congressman will meet with members of the Nevada finance team on Tuesday evening - his first such event as part of Mitt Romney's campaign - but members of the media will not be allowed to attend.

Romney himself held a meeting with Adelson, this campaign season's most prominent donor, at the same hotel in May, but it was not certain that Ryan will meet the billionaire.

Adelson has yet to contribute directly to the Romney campaign, according to the latest disclosure filings, but the magnate and his wife, Miriam, have donated $10 million to the outside "Super PAC" group backing Romney.

During the primary season, Adelson and his family spent $21.5 million to support another Republican candidate, Newt Gingrich, who dropped out of the race on May 2.

The gambling magnate's business empire is under review by several regulatory bodies that are looking into his casino powerhouse Las Vegas Sands Corp and its operations in Macau, the only place in China where casinos are legal.

Sources familiar with the probe this week told Reuters the Nevada Gaming Control Board is investigating whether the company broke bribery laws through its dealings in mainland China.

That probe is on top of reviews by the U.S. Department of Justice and the Securities and Exchange Commission, which the company confirmed in March filings.

Las Vegas Sands has denied illegal activity.

The Romney campaign has allowed reporters to cover fundraisers as long as they are in public venues and not at private residences, but an aide said Tuesday's event in Las Vegas was different because it was not a fundraiser but a "finance event."

(Additional reporting and writing by Alina Selyukh. Editing by Alistair Bell and Christopher Wilson)