It depends what the REW is masking (and if you have the genetic history, you should be able to know this), but you won't get any BEWs but each kit has a 50% chance of inheriting the vienna gene, so has a 50% chance of being a vienna. BEWs are only 'made' when a rabbit inherits two vienna genes- as I understand it.
There is a sticky in health about responsible breeding, so that would be worth a read.