I am not a lawyer, but to my mind it is free for you to develop your product with OCCI.
You would use the OTN license to devlop your app: http://www.oracle.com/technetwork/licenses/standard-license-152015.html
Its the end user's who would pay the license fees for Oracle.
By the way, most people who know Oracle would not be too keen on a data backup via an API like OCCI - they would normal Oracle backup procedures e.g. via RMAN, which allows recovery to any point in time.