I have a couple of thoughts.
I have made lots of BL bows and really like the wood. I have seen that powdery wood.
I've never used standing dead wood of any kind. But BL heartwood is rot resistant for sure. I still would not use standing BL deadwood. Also, that does not mean the wood is dry.
There is an insect that gets at the wood here in NH and makes it powdery. I guess one should remove the bark and sapwood asap. LOL. But who does that?
The other point is the stave should be sufficiently reduced in weight before stringing it for the first time. I prefer 10# over final draw eight but 20# is ok.
If you can do that by feel when floor or long string tillering then fine.
I can't so I developed a method where I long string tiller out to 10 in of string movement looking for 5# over final draw weight for a 26" draw and good limb movement. This puts the stave around 10# over final draw weight.
There are buildalongs on my site.
http://traditionalarchery101.comJawge