Do high power through hole resistors need a heat sink
Typically power resistors are designed to operate without a heatsink (or have one built-in). If the manufacturer recommended use of a heatsink, it would be covered in the datasheet.

That said, they can get quite hot, so care should be taken to keep temperature-sensitive components away from a power resistor that is dissipating a lot of heat. Additionally you may want to ensure that the resistor is mounted with an air gap below it as well (not touching the PCB) to promote air circulation on all sides.

A surface mount power resistor with a pad for heatsink may require a copper pour/heatsink or a physical heat sink of some kind attached (see the datasheet for the component in question).



Typical power resistor



Power resistor that incorporates a heatsink