Seems like it would be unnecessary, but I'm wondering if I can or should crumbcoat under white chocolate ganache, using a very, very thin layer of BC? Last time I used a white chocolate ganache over a dark chocolate cake, the crumbs nearly drove me mad!!

Will it hurt or help?

I always crumb coat just because it creates a smooth surface. No cakey lumps or bumbs.

Ditto Chef Debi (Yes, Deb, that's what I'm calling you from now on lol).