Can women greet men hello by shaking hands?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

If what you mean is that she shakes hands with men who are alien to her, i.e. not Mahram, then this is unlawful. For more details, please read Fatwa: 82318. If what you mean is that she waves with their hand when greeting men, the rule of this issue is in the Fatwa: 82299.
Allah knows best.