You are correct, camber isn't required for them to work. It is required for them to work properly. Even your Dexter video shows the bow in the axle. If you notice that your axle mount is very close to the torsion arm which means the amount of camber (bow in your axle) will be less than one with a longer distance. It doesn't mean that your mount won't work. I'm just cautioning folks not to reinforce the center section of the factory axle mount at the point where it is made to flex. I'm not refering to the frame assembly that the axle mount attaches to. That part should be as strong as you can reasonably make it.
Also, from your pictures, it doesn't appear that the factory axle mount failed, it appears that it's attachment to the frame is what failed.
For those folks replacing axles, the Flexiride axles are what I have used almost exclusively for many years because they are the only ones that I know of that use a splined torsion arm so that you can adjust the axle torsion arm angle by just removing one large bolt and each spline will adjust the angle by about 6 degrees. It makes changing height (within reason) very easy. I used Dexter and Hayes (now Al-Ko) in the past, but Flexiride is much more adaptable. As far as making axles, you can buy them much cheaper than you can even buy the parts for them anymore. Southwest Wheel in Texas is a good supplier for the money.