The Nazgul. Men?

[Kuruharan]

The Chief of the Ringwraiths lived in Minas Morgul, and Gothmog was the name of the Lieutenant of Minas Morgul. Possibly the same individual?

If you mean what it looks like you mean, that the Chief of the Ringwraiths and Gothmog were the same individual, then the answer is no. The Witch-king was killed before the name Gothmog was mentioned in ROTK.

And if you mean that Khamûl and Gothmog were the same, I find that unlikely since Khamûl was the lieutenant of Dol Guldur and Gothmog the lieutenant of Minas Morgal.