Saturday’s military parade in Washington celebrating the 250th anniversary of the U.S. Army was sponsored by at least four brands that have strong financial and political ties to President Trump, raising questions about whether the event benefited his allies and supporters.

Attendees who sought relief from the sweltering heat on the National Mall found free cans of a new energy drink brand sponsored by Dana White, who is the chief executive of the Ultimate Fighting Championship and one of Mr. Trump’s staunchest allies.

Palantir, the data analysis and technology firm whose contracts with the federal government are expanding, and Coinbase, a cryptocurrency firm that donated to the president’s inauguration, also sponsored the event. Oracle, a database company whose co-founder is a close friend of Mr. Trump’s, received a shout-out on Saturday as a sponsor.

U.F.C. was mentioned as a sponsor during the military procession and on the event’s website, but its spokesman said in an email statement that the company was not a corporate sponsor and that Mr. White had supported the program in his personal capacity.

Federal regulations prohibit the use of public office for the private gain of officeholders or their friends, relatives or nongovernmental affiliates, said Richard W. Painter, who served as the chief ethics lawyer in the White House Counsel’s Office under President George W. Bush.

“The parade is being used for advertising by these entities with close business ties to the president,” Mr. Painter said in an interview. “You’re in a situation where the U.S. government has been used to endorse a product.”