Always check their baggage faq, they usually have different exceptions for snowboard/ski equipment.
This is from their special/fragile baggage section.
Baggage Chart - Frontier Airlines
SnowboardOne item which may include one snowboard, one set of bindings, and one pair of boots. One pair of boots (in a boot bag) may be checked separately from the snowboard, but still count as one item.
- One snowboard bag and one pair of boots = one item
- One piece of luggage, one snowboard and one pair of boots = two items
Excess and overweight charges apply if applicable.
Oversize charges do not apply
Carry-on: Yes; Boots onlyYes, if not packaged in a hard-sided case
I bolded the Oversize charges do not apply. That's actually pretty good, some airlines may still have size restrictions even if it's a big snowboard bag.