@Rose Quartz, I trust your avian vet as well, and think its very interesting that it doesn't spread through the egg to the babies.
I highly suggest you inform your clients of the situation though. Even though you'll be 99.9% certain they don't have it, its still good to tell the people that your only 99.9% sure.
I had that happen to me after I bought hatching eggs from someone with a Mareks infected flock. Same thing, the contagious dander on the egg shells can infect the chicks if it survives the incubation process, and when I touch the eggs that dander gets on my hands, meaning I could infect my flock that way. The seller didn't' tell me any of this, and I found this out after he posted a thread about it on here, I was very angry.
I'm just suggesting that you tell your clients you have an infected flock, and they should also probably wash hands/change clothes before touching their flock.
I'm so sorry your going through this, its a total bummer.