Can a company legally layoff a large number of employees and then hire new ones for the same jobs? (Ohio)?

Yes

Keeping in mind, they will be paying unemployment for all the employees they laid off. There is no legal obligation to keep an employee.

This is why unions exist, because generally the government always favors entrenched interests who write checks.

That is what happens when Obama-Care and cheap illegal alien labor are permitted and make normal salaries and benefits unprofitable for the company. I hope any company that falls into the Democrat Trap and does that fails due to lack of good employees.

Yes but a class action can still be brought by ex employees if it was seen as discrimination in hiring practices. Discrimination is not always about race or sex. Before you act look up any laws about such a law or class action suit in your state and save some time and maybe money.

Yes, they sure can.

The only thing that would be illegal is if it were proven that the layoffs were specifically to persons in protected discrimination classes (race, religion, national origin, gender).

Yes. They can hire and fire whenever they wish to do so. Especially in Ohio which is not a right to work state.

Only if the laid-off people are white.