The answer is maybe. Polynesian had several styles of stairs over the years. Some have sharp edges and corners and lend themselves to being covered by vinyl. You can see an example of this in our Polynesian Pool post .
Many have rounded edges and corners and cannot be covered effectively. Trying to cover these most times leads to wrinkles and a poor fit. This is obviously a project for a pool professional and you should depend on him to decide if your steps can be covered with vinyl or not. In most cases, our best recommendation is to add faceplates and gaskets around the step perimeter and not have the liner cover the steps.
In all three of the examples shown below we would recommend using step faceplates and not trying to cover the steps with vinyl.