Ok, I will try to answer your question from my point of view.
Which type of currency is better for paying employees? Is it Bitcoin or Fiat?
It depends on the employees. Some employees don't know and even care about bitcoin. Few more employees know about bitcoin. So, Employees who don't know and care about bitcoin would be better off getting paid using fiat. Because it's useless to give bitcoins to people who don't know how to use them.
Do you think we'll be able to see more jobs paying Bitcoin in the future? Or will Fiat still dominate the jobs industry?
I don't think so. Unless they work with the bitcoin community. As we know that companies in a country will comply with the laws that have been set by the government. If a country prohibits payments (including payroll) using bitcoin, the company will not pay salaries in bitcoin.
Is working for Bitcoin just like working "under the table"?
This is very subjective. I can't answer for sure