I am backing up my Macs on the Time Capsule, the Apple store staff told me that I would also be able to backup other decives to the Time Capsule. I have two non-Macs to backup on the Time Capsule:
2) an external drive that stores my iPhoto library.
You can backup an iOS device to either iCloud or to iTunes. If your iTunes Media folder is located on the Time Capsule, then the backups would reside there as well.
For the external drive: Time Machine can backup any HDD physically attached to your Mac. The destination of those backups can be the Time Capsule.
The iPad backs up to iTunes on your computer, or to iCloud. If you are backing up to iTunes, when the computer backs up, the iPad backups in iTunes are backed up as well.
It is not possible to backup the iPad directly to the Time Capsule.
To backup the external drive that is connected directly to your Mac via USB or FireWire....
Open System Preferences (gear icon on the dock)
Open Time Machine
Here, you will see the list of items that are excluded from backups at the current time
Click the drive containing the iPhoto library to highlight it, then click the - (minus) button to remove the drive from list of excluded backup items
Time Machine will back up the hard drive on the next pass along with your Mac