Adding an App to ICloud

The App itself needs to support saving data in iCloud for it to be saved to iCloud and appear in iCloud settings.

If it does not appear there, it means it does not save data in iCloud and you cannot make it save it there.

You should be backing up your iPad regularly to prevent data loss in the event of a crash. With a backup, all saved data can be restored to a device.

A backup, whether its done to iCloud (not the same thing as having an App save data directly to iCloud), or iTunes on a computer, saves all the data from the iPad including App data if stored locally.

See here: About backups for iPhone, iPad, and iPod touch - Apple Support

and here: How to back up your iPhone, iPad, and iPod touch - Apple Support

Just to clarify. If my iPad were to crash, everything in this app would be lost?

I just need to know if I have to save all my bookmarks another way.

If you want to be 100% sure, you may want to contact the app developer or check their resources.

They are the party who decides to put the app's data in the correct spot to be caught by iOS's backup processes.

Although unlikely, it's possible the app's data is not backed up and only the developer can confirm this.

The backup process backups up all data on a device that is not being saved to iCloud already.

Development wise, there is no place to put data that the backup process cannot get to. There's no possibility of the data not being backed up if its not being synced to iCloud by the app already.

The only time the backup process does not backup data from an App is if its already being saved to iCloud. If it is, it will appear in the App list in Settings->Account->iCloud with a switch to turn the option on or off for that app.

If its turned off, then the backup process automatically backs up the app data, to iTunes or to iCloud.