Yup, the Navy guarantees you get a shot at Pilot or NFO. Making it through the training is another story. Also, since, unlike ROTC or Academy guys, the Navy doesn't consider OCS types to owe them anything. So if you fail or DOR out of training, you won't get another shot at another designator(any more... they used to send guys SWO). If you're an Academy or ROTC type and can't make it through flight training, they'll stick you in some do nothing busywork job somewhere to finish out your four year commitment... but if you're OCS, you'll get a ticket back home and an administrative discharge. Correct me if I'm wrong.
Hijack: Off topic, another thing about OCS is that the Navy uses OCS as the equalizer for officer quotas. The system guarantees that every year, a near exact amount of Ensigns will be commissioned through ROTC and the Academy. If the Navy doesn't need that many officers that year, they cut back on the number of OCS classes. In my year, 2000, they graduated a class at least every two weeks, and for awhile, every week... now I hear they're down to five classes a year (somebody correct me if wrong). Which makes it more competitive as far as test scores to get a contract. I'm glad they were hiring on the spot when I decided to join.