In IBM BPM - Oracle setup Running a system service or Instantiating an instance is no that difficult. Following is one of the several ways we can do this.
1. Create a system service that has code that starts a BPD in a specific snapshot and expose this service as webservice. Please check below link for how to start BPD process using javascript( IBM BPM guru Neil Kolban)
https://developer.ibm.com/answers/questions/164084/how-to-start-a-process-from-javascript-in-a-named.html
2. Oracle 11i has "web api" using which we can invoke webservices. Implement a stored procedure that perform webservice invocation and then create an "oracle job" which invoke this stored procedure and schedule it to run as desired. We can also implement exception handling in this Stored Proc and generate an email on failures.