Do unused floating holidays need to be paid out upon termination?

It depends on state laws. For example, in California, if floating holidays can be taken at any time, they are considered vacation days. That means they're essentially the same as earned wages, meaning employees are entitled to payment for them upon termination.

Regardless of legal statutes, though, respectful, professional companies will always pay employees for unused PTO of any form, because it's fair and the right thing to do.