Here is the exact wording.

Ski and snowboard equipment are allowed as checked baggage. One ski/pole bag or one snowboard bag and one boot bag is accepted per person. The combined weight of the ski/snowboard bag and the boot bag may not exceed 50 lbs. or excess weight charges will apply. Linear dimensions may exceed 80 inches (203 cm) without excess size charges. All standard baggage charges apply.

As with everything else, exceeding the weight limit or using your ski bag as a clothing suitcase, are a matter of risk tolerance. Worst case, you pay extra.