Just so I understand you want to do a 6.1 system with 5DBs as the sides and a 5C as the rear speaker?
If that's the case, I think the 5C would work fairly well for that application as your rear speaker and the 5DBs are excellent side speakers and are ideally placed directly to your sides about 5-7 feet off the ground.
As long as by flush mounted you mean the back of the speaker is up against the wall and don't mean that they will actually be inside the wall then I think your proposed set up will be great.
I hope that helps but please let me know if you have any other questions!
The Verus DB will use its own hanger like the 5DB or 4BP. I suppose you could mount it from the ceiling if you really wanted to. I don't have a weight yet for those so can't recommend anything in particular. They would work better if mounted on the wall directly to the left and right of the listening position and about 5 to 7 feet up. If that is not an option and they have to be mounted from the ceiling directly to the left and right of the listening position and angled down, that should work as well.
Matt, I posted a post in the speaker forum on this site showing a diagram of my family room where my HT is. As you can see, I do not have a left wall (based on the couch) due to it being open to the kitchen. Thus, for that side, I will need to mount it to the ceiling as stands are not an option (two Jack Russells and WAF issues).