Can he give zakah to one of those who are working for him?

Allah has stated the eight categories to whom zakah may be given, in the verse (interpretation of the meaning):

“As-Sadaqaat (here it means zakah) are only for the Fuqaraa’ (poor), and Al‑Masaakeen (the poor) and those employed to collect (the funds); and to attract the hearts of those who have been inclined (towards Islam); and to free the captives; and for those in debt; and for Allah’s Cause (i.e. for Mujaahidoon — those fighting in a holy battle), and for the wayfarer (a traveller who is cut off from everything); a duty imposed by Allah. And Allah is All-Knower, All-Wise” [Al-Tawbah 9:60]

If this worker falls into one of these categories, such as if he is poor or needy or in debt, then there is nothing wrong with giving zakah to him. 

But it should be noted that it is not permissible for the owner of a company to give zakah to his workers instead of other rights that his workers have, or in return for the worker doing additional work and so on. 

Imam Ahmad (may Allah have mercy on him) said: The scholars used to say concerning zakah: It should not be used to pay debts or to favour a relative or to protect one’s wealth (save money). Al-Mughni (3/153). 

i.e., instead of giving the worker his due of an increase in salary or a bonus or payment in return for additional work and so on, he gives him zakah. 

Shaykh ‘Abd al-Rahmaan ibn Jibreen (may Allah have mercy on him) was asked: There is a person who works for me, and I have heard that he is in debt. Is it permissible to help him by giving him my zakah? 

He replied: It is permissible to give him your zakah so long as he is unable to pay off the debts, or if his income leaves nothing to pay his debts with after he has spent on his family, or if your aim is not be to encourage him to work or to be honest in his work for you, and you do not decrease his salary or give him more than he needs."(Fatawa ‘Ulama’ al-Balad al-Haram  p. 174). 

He was also asked: There is a commercial company among whose employees are those who are entitled to zakah; what is the ruling on giving them some of the company’s zakah?  

He replied: If these employees are Muslims and poor, then there is no reason why they should not be given zakah, but it should be in accordance with their entitlement, and it is not permissible to make it like a salary or reward for their work, or to intend thereby to win their sincerity and make them stay in the job. It is better to give it to the employees secretly, or via a third party, so that they will not realize that it is from the company, so as to avoid falling into a grey area. And Allah knows best. 

Fatawa ‘Ulama’ al-Balad al-Haram (p. 174).