Yeah I would agree that its a bad idea. The issue is that if you get a black and white gecko that had a chance of being one or all three types of snow you couldn't tell which it had or didn't have and therefore couldn't state what genetics it had which would be the issue that people are frowning on.
I've seen it done but wouldn't recomend it. You wouldn't know what the heck kind of snow you had. And the results I've seen don't come close to nice line breed snows.