I gather that this is supposed to be a humorously rhetorical question: “Now, am I saying this to you: make friends for yourselves by security of injustice, so that when you fail then they will be accepting you into the tabernacle of God’s own?!” No, of course that isn’t His point, as He goes on to explain. It’s a somewhat typical rabbinic how-much-moreso comparison: even this ridiculous and/or evil situation demonstrates admirable cleverness (I don’t think the accountant has been slandered, by the way), so how much moreso should good people be good about better things.
In this case the moral is, “If you cannot be trusted even in regard to unjust security, who will entrust the good things to you?” That doesn’t mean you’re supposed to go out and deal in the security of injustice – thus the wry rhetorical question introducing discussion of the parable.
It would be like saying even the Mafia treasures friendship and loyalty, so how much more should good people be loyal and friendly. Now, am I saying you should go out and join a mafia gang? Of course not.
Jesus makes such comparisons with some frequency in the Synoptic reports; for example, if you only do good things for those who love you, what more have you done than other people? Even pagans and traitors do that!
I suspect Jesus might also have intended a comparison and contrast between this embezzler and His other parable about an embezzler caught by his master: this one, even in his wickedness, at least wants to be merciful on other people. He has a twisted and self-serving understanding of mercy, but he does have one! – so shouldn’t the children of light be even better at mercy than this unjust man? Whereas the other embezzler, once shown mercy and all his debt had been forgiven, only saw an opportunity to further profit by going out and using the supposed excuse of his debt to squeeze people who owed him, sending them into the punishment he had already escaped when they couldn’t pay up. Therefore, in just the same way, your Father in the heavens will be doing to each one of you (talking to the apostles, up to and including Simon Peter), if you are not forgiving your brother from your heart.