I doubt the Predictamancer was in league with Dove and Charlie. While the Prediction concerning Weatherbug was for an imminent attack, the one about Homekey was open ended. If King Posbrake had not chosen to hire Dove, the attack may not have occurred for a hundred turns. While it may seem like too much of a coincidence that the first caster Digdoug ran into was a Carny, I find it likely that Carnies that are desperate for upkeep may loiter around Portal Park, looking for marks to make a few quick schmukers, even if it is only be introducing them to others.
It does seem obvious, though, that Dove and Charlie already have some sort of working relationship at this point, since she made the introductions between Homekey and Charlescomm. Also, Charlie is willing to lose of archons. There is a standard clause calling for reimbursement for archons that are croaked. For an extra charge, that clause can be waived. Homekey is not a wealthy side. If they are too successful in repelling Charlie's attack, it may end up being very expensive for them. I think Posbrake is going to be hoisted by his own petard. As his brother mentioned, he is very fond of honoring the letter of his agreements while violating the spirit. Charlie is a master of this. While Charlie wouldn't do something as flagrant as working for Delkey or Numloch while under contract for Homekey, or failing to honor the terms of the contract. He may, however, fail to mention that his archons detected a large air force massing in striking distance of Homekey, since he wasn't paid to provide reconnaissance, at least not initially. If Homekey uses all of their tower defenses on the fake attack, they'd be in bad shape to repel the real one. Of course, Charlie's archons will be close by, and able to help, for the right price. Charlie wants the same thing Dove wants, to get every schmucker he can from his clients. While this may not end badly for Homekey, now that Charlie's involved, it won't end well, either. The only thing we know for sure is that, by the time of the main comic, Dove is still a barbarian in the Magic Kingdom. So, whatever happens, she won't be joining Homekey.
As for how Dove is cooking the books, the rule she is breaking may be as simple as "Only factual information may be entered into the ledger." Delkey already has a record of Homekey's expenses and income, so she can't be fudging the actual numbers, but she may be changing a line item such as "Hire a Predictamancer" to one or more items which are less objectionable, such as "Hired a Dollamancer to produce new raiment for the King". I think the explanation of Carnymancy that Dove gave was a much for the fans as the characters, and until such time as it is revealed otherwise, I think it best to work under that assumption.
मृत्युः सर्वहरश्चाहमुद्भवश्च भविष्यताम् ।