Is not informing the manager of everything that goes on in the department, which may lead to problems or deprive some employees of their annual raise, considered a dereliction of duty, even if the work is performed perfectly?

If you are responsible for employees, the fundamental principle is to follow up on their conditions. If they commit a breach of work or a shortcoming, you should inform the management of that after advising and alerting them. You must be careful not to commit injustice or fawn by making a false complaint. Be gentle with them so that you may attain the supplication of the Prophet, peace and blessings be upon him: "O Allah, whoever is given charge of any affair of my Ummah and makes it difficult for them, make it difficult for him; and whoever is given charge of any affair of my Ummah and is gentle with them, be gentle with him."