BR shooters will believe anything they are told if it comes from a source they want to believe.
I have seen no evidence to indicate that bluing has any adverse effect. I have shot quite few CM match barrels which were blued and they were among my most accurate rifles. Having said this, if I test a CM barrel, in the white, and it shoots exceptionally well, I am too much a coward to blue it!
As Butch pointed out, it is rare to see any serious BR shooter using a CM barrel. Barrelmakers make their select match barrels with SS because they can more easilt produce a very good barrel.
I used one CM barrel which was competitive but that was over thirty-five years ago and competitive then and now are different animals. Aggregates in the mid-2's were just fine in the mid-to-late seventies. Today, the same agg won't make ya puke but it probably won't win you much either. GD