If you are getting a lot of guests who fly in, then its unlikely they will be carrying a portable crib. I guess if it's going to garner you more bookings to have that amenity avaialble, and if your location compitition does not, then it may be worth the investment of a portable unit to have on hand along with 2 fitted sheets? I suspect they will be carrying their own blankets for this child, so that probably isnt necesaary.
A portable will fold up and can be stowed neatly when not in use, so if they bring one, then great, if not you can list it as an additional amenity, however, I would stipulate it is a portable only (if that's what you choose to purchase) and perhaps take a photo of it popped up to have on hand should they ask? Portables typically are considered appropriate for children under 2 years. Make sure you purchase one after research to make sure it lists no manufactures defects or recalls for saftey.