The acceptance in Nixon's mind was probably not an admisssion of wrongdoing however in reality if such a thing could be applied to Nixon's world - it would come the closest to an acceptance of wrongdoing.
Although Ford totally blew how he went about doing the whole pardon thing. This was and will remain a point as conspiracy theorists will say was a deal Nixon and Ford struck. Others that Ford should have known better on how to get some tepid warmed-over pre-approval after all his years in the House before forging ahead. He probably did the right thing but used the wrong way to do it. Ford did not want to see a former President of the US in a criminal docket on the witness stand being grilled by prosecutors.
The acceptance of the pardon would probably come close to the legal saying of no contest or as it is called: nolo contendere. The definitions is: in criminal law a defendant's plea in court that they will not contest the charge of a particular crime. In the Nixon case while he had not beeen indicted the indictments were pending as well as consideration of impeachment.
By stepping down from the presidency he could not be charged with those crimes as the president - high crimes and misdemeanors - but based on what charges were being brought forward he could be still tried as a private citizen for previous indictable offenses whether civil or felony.
The acceptance by Nixon meant no charges could be brought for whatever charges were going to be brought whether in the Senate under impeachment proceedings or in court under what would hav been criminal proceedings.
While technically not an admission of guilt for commission of the crime, the judge will treat a plea of "no contest" as such an admission and proceed to find the defendant guilty as charged. A "no contest" plea is often made in cases in which there is also a possible lawsuit for damages by a person injured by the criminal conduct (such as reckless driving, assault with a deadly weapon, aggravated assault), because it cannot be used in the civil lawsuit as an admission of fault.
"No contest" is also used where there has been a "plea bargain" in which the defendant does not want to say they are guilty but accepts the sentence recommended by the prosecutor in exchange for not contesting the charge (which is often reduced to a lesser crime). It is standard practice for the judge to ask either the attorneys or the defendant, "Is there a factual basis for the plea?" before accepting it and finding the defendant guilty.
Nixon basically plea bargained the charges in exchange for the presidency - afterall as Nixon said; " I am not a crook ". But he sure gave a good example of a con - a perp - a skell - a suspect - a person under consideration - and someone who would be asked to come on down to the station house - to answer a few questions.