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^^ This.
Also, I’m not sure what you mean by coaxial in that context. Concentric maybe? If so, that won’t be an issue either. As long as the BB she’ll has been faced off properly then it’ll be fine.
jj72-
I think coaxial is the right term. Non coaxial objects don't share a common axis, so if the BB cups are not coaxial then an imaginary line drawn down the axis around which the drive-side bearing spins would not be the same line around which the non-drive side bearing spins. This means that when you force the axle through them, one or both of them will be receiving a twisting load (in addition to the expected load). In a square-taper BB the bearings are held coaxially by the BB shell, but with independent BB cups they could be not coaxial.
I think the concern was that even if the BB shell had been faced then the introduction of the bracket between the drive-side cup and the frame could misalign the cups, since the bracket is not very finely engineered and is subject to other loads from the chain guard that it's attached to.
ffm
That mounts like an e-type derailleur right? So it shouldn't be a problem.
Only thing I'd be concerned about is the thickness of the plate reducing the amount of axle the NDS arm clamps down on to.