If the vendor says their product (chc) has been pre-washed, then you have nothing to worry about.
I have been using chc from repotme.com for example, and they claim that they wash chc they sell.
I always use straight out of the bag for my paphs (mostly) and others, and never had any problem.
I second that, I always use repotme. com's out of the bag and never had an issue for oncididiums and dendros.