What is the difference between a mole ratio and an empirical formula if there is any?

By definition 'empirical formula' is the smallest whole number ratio of elements in a molecular formula. The 'whole number ratio' is the mole ratio of elements in formula. It is best to keep in mind the definition of 'molecular formula' in contrast to 'empirical formula' which is the 'actual' whole number ratio of elements in a molecular formula.

Example: CH₂ is a 1:2 mole ratio of carbon to hydrogen (smallest whole number ratio) and empirical formula for the 'molecular formula' C₂H₄ (ethylene) whose 'actual' mole ratio is 2:4 = > 2 moles carbon and 4 moles hydrogen in one mole of ethylene molecules.

Also, keep in mind that an empirical formula may also be the molecular formula. Example = > Methane (CH₄). the subscripts are in the smallest whole number ratio (empirical formula) and in the 'actual' whole number ratio (molecular formula) for the methane molecule.