Is it permissible for a woman to greet her great-grandfather's brother with "Salam"?

The paternal uncle of the grandfather is a mahram (unmarriageable kin) to the woman because he is considered an uncle. It is permissible to greet him and shake his hand, as he falls under those exceptions mentioned by Allah the Almighty in a verse from Surat An-Nur: "And let them not expose their adornment except to their husbands or their fathers or their husbands' fathers or their sons or their husbands' sons or their brothers or their brothers' sons or their sisters' sons."