I put one on a MAK 90, and a Saiga.  If you ride the bolt forward gently, the hammers hold the bolt open by pushing on the bottom of the bolt.

Is it normal to recontour the top of the hammer?  BHO is a nice feature, but I dont want to wear out the bolt mechanism.

That is normal and won't wear out anything.

Since the rifle does not cycle the carrier gently on it's own, it's a non-issue.  Jerk that carrier back, let 'er fly back and see if it hangs.  This happens in a few tenths of a second during normal operation.  If you have a problem when you actually fire the rifle, that's when you should examine the parts.  You should not need to be grinding on a Fire Control Group (unless it's a Century set...).  The most you should ever need to do is to lightly polish the contact surfaces.  If you just shoot it a lot, the parts will polish themselves eventually.

You won't wear anything out, as the hammer is under spring tension and can move down when the carrier travels forward over it.