You'll probably find that it depends on the driller himself, and his personal preference. Some of them don't mind, some see it as disrespectful and a sign of no trust.
Personally, I don't mind at all. When I'm drilling a ball for a customer not a single thing changes my level of effort, or amount of care for customer satisfaction.
That being said, there is a downside. The only issue I have is when customers bring me a ball to drill that either will not work for them, or has terrible specs. Most of the time I'm able to figure something out and make whatever they brought me work, but you see where this would be a challenge. For instance, I had a two hander who wanted to start playing straighter bring me a storm sync the other day. It had great specs, but you see where that was an issue.
Anyway, best bet is to ask him if it bothers him. My opinion, it shouldn't. If i can make some money off of an internet ball, or no money...guess which I'm choosing? Hope this helps.
Matt