I am playing and mostly winning at six-handed $5 and $10 DoNs on Ignition. I have played and enjoyed hundreds of these tournaments, but I am concerned about possible collusion at higher limits. This format was tainted by a major cheating scandal at Poker Stars, and PS decided that DoNs were just too vulnerable to cheats and scrapped the format.
What is the honest opinion of DoN players here? Is cheating a problem with this format at Ignition? If so, at what buy ins? Thank you for reading and for your insights.

I don't know about Ignition games (is it anonymous?) but cooperative game theory and especially implicit collusion is really dominant in these games, as you go up in stakes this gets more prevalent (as the players are better) and likely can be mistaken for "cheating" for novice players...

As for the Stars scandal, there was a Chinese firm sharing cards, this can be easily detected by the sites and they executed it badly. They have retreated the format and came up with Fifty50 games which give a better look and incentivizes reg on reg play.

p.s. I was one of the guys who got hit by this as a real blow even though I didn't play high stakes but 10.4s and 20.8s

Yes, Ignition has anonymous games—both cash and tourney.

I would like to focus on what is most profitable for me. And I am uncertain as to the viability of DoNs. Limit hold'em was always my best game.

Very small EV in this imo. I don't think someone will waste his time for this. Maybe if they know each other. From the forums maybe...They must be friends as well. I think this will be pretty rare. Sharing cards...Almost no EV in this. For Hold em. For two players almost no EV. For several... Maybe...But still very small EV. I think this is just a "myth". But I don't play $100, $50-$60 small sample. Who knows...But for $20 no such things. Even if I see that, this will be only funny for me. Don't care really...

For $5 and $10, the most of the regs don't know what they are doing. Many of them play with strategy for "normal" STT. You can't "see" them very often. For a long time. You can't see him as reg. He play so bad. I mean for DoN. And you talk about "team game". Mate, this is very unlikely. And why you care about this!? Whatever...This will be very rare. With such a small EV. And -EV spots exactly for you.

The real challenge there would be actually getting away with it for any significant amount of time. They'd have to thread the very small needle's eye between "advantage" and "obvious" (probably insanely difficult to do, if even possible), and at that point, it would almost certainly involve less effort to just learn how to beat the game straight up than try to play with a large group in a way that can avoid site detection while still increasing ROI.