Cars _with_ traction control ( ASR / ESP ) have speed sensors at each rear wheel hub that read from the outer CV joint.

Cars _without _ traction control have a single speed sensor at the differential pinion.

What you want to do will work as long as the diff ratio and physical dimensions are the same. If the diff ratio is wrong, you might get computer errors as the trans and engine computer are expecting a certain ratio.

Making the swap in the other direction will lead to loss of rear speed signal and ABS errors. ( From what I've read it appears the speedo reads from a front wheel but don't quote me on that. )