Is it permissible to inform a superior about colleagues' transgressions at work, and is this considered a betrayal of them?

Your duty is to advise your colleagues to stop these forbidden acts and warn them that you will report them if they do not desist. If they stop, then that is good and excellent. Otherwise, you must inform the official to take whatever action he deems appropriate concerning them, for the Prophet, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand; if he cannot, then with his tongue; if he cannot, then with his heart—and that is the weakest of faith." What your colleagues are doing by registering attendance while being absent is falsehood and deception, and your condemnation of it is not treachery but rather truthfulness and trustworthiness.