There is no specific BADi for this, but you do have a number of options:
1) You could trigger a workflow template based upon the admissions execution. You would need first to model an event called 'ADMITTED' (for example) on the Business Object 'PDOTYPE_ST'.
2) You could wait for EHP3 (ramp up begins in December), where we will provide a mass-process for setting holds and customer statuses. You could then just periodically set the holds/statuses for all student that meet your specific admissions criteria.
3) If your admissions process is already automated via Workflow, then you can insert a step to create the statuses. This would of course only get triggered via the admissions workflow. If you went directly into the student file and admitted someone, then you would not see any behavior.