+1, in a word.
The Vector is a branding of the Atra that is sold cheaply in China. It takes Atra blades, generic twin-pivot plus blades, and anything else made to fit Atra exclusively, or to fit Trac II and Atra.
No. Only blades like the personna twins which are specifically designed to be compatible with both can be used with both. I think there may be adapter plates available as well, but I haven't used them. The native Trac II uses a twin rail system, the atra used a click in system.
The Vector works with Atra blades but I can't say I'd recommend it. I snagged one last year and it has the weight and build quality of a disposable razor.
The plastic for the Trac II slides blocks the pivot when the dual compatible carts are used on an Atra, so they don't have the same pivot range as dedicated carts.