Cabin camping does not count as a campout for Second Class / First Class rank 1a. or Camping merit badge requirement 9, but it could count for other things, such as the National Outdoor Awards.
In the campout name, you could add something that indicates that it is cabin camping. Something like:
Camp Grenada [cabin camping - 2 nights]
In the Campout Details, you can add notes. You can choose to include the nights of camping or use 0 for the number of nights, depending on how the Scoutmaster wants nights of camping to be counted.