If you're going to use a blade I'd use the thinnest one you can for the centre join edge, ideally something like a razor blade or a scalpel that's flat on one side. If the blade is thicker and has a typical tapered edge it could create a slight 'v' around your cut making it harder to get a clean smooth join. Cutting from the 'back' of your veneer may help too.
(my experience is limited to cutting headstock veneers, so take that into account)
