Violin or Acoustic

 Anyway, I don't see why you wouldn't seal the blade, I apply a somewhat thin, but not too thin, layer, then I sand the crap out of it after letting it dry for at least 5 hours or so.  It doesn't change the blade's playing characteristic at all, at least not with the amount I sand.  I use 300 grit paper and sand it all the way until I see sawdust, so that I know the top layer is completely sanded off.  But polyurethane soaks into the wood slightly, so what you're left with is a top layer that's a wood/sealant mix.  The woody part makes sure the rubber stays glued, and the sealant layer makes sure that all the woody parts stick together.  What you get is perfect rubber attachment with zero splintering   My blades don't look like they've been sealed at all, and it doesn't feel like it when you run your finger across them either, yet whereas before it would splinter every single friggin time I remove a rubber, now I don't get even the slightest splinter.  Maybe some blades, like perhaps the Violin, is pretreated this way?

Personally, I don't think slight uneven-ness is a problem.  300 grit is pretty fine to start with, so it's unlikely to create any significant uneven spots, plus both the glue and the rubber are much softer than wood, so they should help mitigate any potential uneven-ness.  I can see why you'd be worried though, and if a blade doesn't need sealing then why bother, right?