Can a company laying off high-paid staff and hire low-paid staff 5 months later to do the same work?

There could be concerns about age discrimination in the US, however if they waited 5 months to open the new reqs and start interviewing, then that would difficult to get them on.

Barring local laws to the contrary, of course.

Its legal...100%

Unless there's a union contract that guarantees laid-off employees first call-back, it's perfectly legal.

Of course & it is perfectly legal as well

if they can do the work, sure

Yes. Employers are always looking for ways to cut costs

Yes..of course.

Yes they can.

Yep. It's done all the time - and not just in the USA.