Is it safe to let apps use Touch ID on an iOS device?
The application does not have access to the fingerprint data stored on the device. The API provided by Apple tells the app if the auth process was successful by a simple yes/no value. No hash is provided. Here's the documentation.

Also the fingerprint data is stored in the device's "Secure Enclave" and is not accessible. 


  The Secure Enclave is part of the A7 and newer chips used for Touch ID. Within the Secure Enclave, the fingerprint data is stored in an encrypted form which - according to Apple - can only be decrypted by a key available by the Secure Enclave thus making fingerprint data walled off from the rest of the A7 Chip and the rest of iOS.


Source: The iPhone Wiki