It's an assumption based on photographs with the Concert, but a direct side by side comparison with the Baritone. The latter was identical save for the Ohana having what appeared to be a shinier back. The photos of the Ohana concert also have a shinier back - but otherwise the build, the top, the decor, the fingerboard (save for the different headstock logo) are identical. I am not entirely sure if the Ohanas have pickups myself. They really are the same thing though in virtually all aspects I can see. It's not just the concept of 'dropping a wood top on a plastic back' that is similar. The actual shapes of these, whilst at first glance are typically double bout ukulele shapes are also quite distinct if you look. The waists are not very narrow giving them an almost teardrop shape i've not seen on any others, and on the baritone in particular, the cutaway is very distinct to that 'model'.
As for others - there was a model knocking about in the UK by Kamoa - the KUC-70b (no longer available) - that is also completely identical to this one save for the headstock, but also has no pickup. Phil Doleman had one and I can confirm it's the same as this Clearwater. Again, note the distinctive shape of the waist (sorry, don't have a better picture)
As for whether these are B stock or not up to Ohana standard I can't see why they are - i've seen about 4 of these Clearwaters in person now, two of which I owned. All were flawless in every department - not a mark in the finish, not a single bubble in the gloss.
Other than that - I have no idea - but what is patently true is that there are far less production lines in China than there are brands!
Can't speak for how the Vita compares as i've not played either.