"Why did Jehovah appoint him as a Ministerial servant?" Dosen't this go against all that the WT has taught people about Jehovah, the Bible, and Jehovah's ways?
To go back to your original question, I would refer you to what the apostle Paul counseled elders when considering recommendations of other men. He wrote: "Never lay your hands hastily upon any man; neither be a sharer in the sins of others..." Because Paul specifically cited the dangers of hastily recommending a man who might not be qualified, it shows that the process is not automatic. In other words, the holy spirit is not going to immediately correct the mistakes of those who recommend unqualified candidates, in that the ones who recommend those who have these concealed sins actually share some responsibility. Hence, it is possible for the elders to become sharers in the sins of others. In the specific case you mentioned the elders do come under some reproach in the eyes of the congregation for having recommended such a man for appointment.
We may however be confident that even though the holy spirit may allow such things to go on, it is only a temporary indulgence. As Paul went on in verse 24 to say: "The sins of some men are publicly manifest, leading directly to judgment, but as for other men their sins also become manifest later." The case in your congregation is an example of how a man's sin becomes "manifest later." / You Know