I think the opposite, but it's just a notion.
If colluder's are in RUSH, they would have to wait a long time to meet each other most of the time. On those rare occasions they did meet up they would need to have a sucker, and if you do much rush, you know most folks are out of each hand early, and most these days are playing pretty decent hands. Maybe not monsters, but by and large, playable hands, not like your normal donkfest IMHO.
While they might try it a time or two, I think they would not be as effective in RUSH as in a normal tourney, or ring game. And truthfully, a couple of colluder's could sit at a short handed table and if they were worth their salt, probably be very effective. And a whole lot faster. And then run.
On the other hand, because so many people don't pay a lot of attention to the rush hand they have already folded to, there would generally be fewer witnesses........
And then maybe in a rush ring game they could find that happy medium where they see their sucker often enough AND each other often enough to maybe worth attempting. Also in the RUSH ring games you can play 4 hands at a time within the same group, which would/could even enhance those rare meetings to be much less rare.
Yup!, I'm convinced, RUSH ring games would be the place to collude.