All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
That which these people do of deceit and trickery by presenting forged details to obtain government benefits is not permissible, as we have clarified in Fataawa 88631 and 142897. The same goes for whoever opposes the conditions of residence and contractual obligations that necessarily allowed him to reside in those lands by seeking gain through their private cars and otherwise, while he is not permitted to do so.
It is an obligation upon the Muslims everywhere, especially in the West, to be role models of truthfulness and of fulfilling observed conditions, due to the Hadeeth: “Muslims are bound to their conditions.” [Abu Daawood]
As for reporting these people, then this could be a means to changing the evil, but it should not be considered until after advising the violators, encouraging them to stop their violations, and warning them of punishment. If they do not cease from their trickery and deception by which they take benefits without right, then it is appropriate to notify the responsible authority if doing so is the way to protect its money from transgressions.
As for those who violate the country's law by making gains with their private cars, then they should be advised to stop. But reporting them could cause a greater harm than their initial mistake as you have mentioned. Moreover, this act they do does not transgress against the wealth of other people, nor does it consume wealth through falsehood, so it is not like the first situation.
Allaah Knows best.