The league said it was satisfied that the Raiders and owner Mark Davis interviewed minority candidates for the position before reaching an agreement with Gruden.
The Fritz Pollard Alliance, an advocacy group that promotes diversity in NFL front offices and coaching staffs, had asked the NFL one week ago to investigate whether Oakland interviewed minority candidates before naming Gruden.
Raiders general manager Reggie McKenzie said that he interviewed two minority candidates before Gruden's hiring on Saturday. Those candidates were Oakland tight ends coach Bobby Johnson and USC offensive coordinator Tee Martin.
The Rooney Rule requires teams to interview at least one minority candidate as part of an open process.
The Fritz Pollard Alliance released a statement Friday, saying it "strongly disagreed" with the NFL's findings and termed the interviews of Johnson and Martin as meaningless.
"We believe the facts overwhelmingly point in the other direction. In his enthusiasm to hire Jon Gruden, Raiders' owner Mark Davis failed to fulfill his obligation under the Rule and should step forward and acknowledge he violated the Rule," the statement read.
The alliance initially had downplayed any concerns of Oakland breaching the rule. That is, until Davis said at Gruden's introductory press conference that he had been trying to bring Gruden back to the city since the passing of his father, Al Davis, six years earlier.
"The NFL broke ground when it created the Rooney Rule, but it made the wrong call in refusing to penalize Mark Davis in this instance," the statement continued. "Davis crossed the line, and we are disappointed in the League's decision. The Rooney Rule and all of the League's equal opportunity efforts need to be strengthened. We have called for meetings with the League to ensure that a process like this never happens again."
Gruden left the broadcast booth at ESPN to return to the franchise where he spent his first four seasons as a head coach. He posted a 38-26 regular-season record (40-28 overall) from 1998-2001 and guided the team to two playoff berths, including appearances in the AFC Championship Game in his last two seasons.
The NFL has issued discipline for Rooney Rule violations in the past. Then-Detroit Lions general manager Matt Millen was fined $200,000 for circumventing the rule when he hired Steve Mariucci as the team's head coach in 2003.