Based on my understanding and experience, there are different types of pools, e.g., (1) "Fully Assessed Pool" in which you have gone through all procedures. If you are in this kind of pool and if there are openings, you could be the lucky one; (2) "Partially Assessed Pool" in which you passed the exam but have not called for interview and reference check. If the hiring manager finds you in the pool and has the interest on you, he / she may call you for an interview to complete the process.
On the other hand, while I know many friends got hired by the Government by being picked up from the pool, I do realize if you know the hiring manager or if a friend of you knows him / her, your chance of being picked up increases significantly, espeically at this time.