Did his supporters refuse to accept any wrongdoing even after his resignation?

No. Many supporters even accepted wrongdoing before his resignation.

After the 'smoking gun' tape was released, his political support completely evaporated. Even the staunchest of Nixon's supporters, including those who voted against all articles recommending impeachment in the House Judiciary Committee, now indicated they would all vote in favour of impeachment on the House floor.

Furthermore, a Congressional delegation told him that conviction in the Senate was a certainty. Only slightly more than a handful of Senators were willing to acquit on the charges laid against him.

The condemnation of Nixon's conduct was almost unanimous and transcended partisan divides. Of course, you could point to a few token individuals who continued to resist impeachment and support him. But the overwhelming majority had left him by that point. Resignation was merely a means to expedite the inevitable outcome of removal from office.