Generally it isn't a problem to touch a blind person on their hand or arm below the elbow to get their attention when getting their attention via sound isn't appropriate or reasonable in the circumstance. I wouldn't grab them, but touching them and then withdrawing is probably going to be OK, again, depending on the circumstances.
It's unlikely a blind person would hear you in a noisy environment unless you were speaking extremely loudly over-and-above the background noise. For a blind person, getting their attention via sound in a loud environment is like a sighted person being at a rave and someone trying to get their attention from across a crowded dance floor. The sense being used is being overloaded by input and is unlikely to notice additional input.
My wife is blind, has a guide dog, and doesn't even like to walk by someone mowing their lawn when she's walking with her guide dog because it's disorienting for her. She gets her input via sound in nearly all cases. And she wouldn't have a problem with someone touching her on the hand to get her attention and then telling her that her dog was doing something it shouldn't be doing.
In response to the comments about guide dogs eating while on duty, guide dogs must have a very high drive to work in order to be good at their job, and it's been observed that their drive to eat is somehow related to their drive to work. Labradors (the breed of my wife's guide dog) have an incredible drive to eat. They will eat nearly anything. They consume a cup of dog food in about 10 seconds, and that's not exaggerating. They are trained to not eat things that have been dropped on the floor, but the hunger drive in them sometimes wins out. It would not surprise me to see a guide dog attempting to eat food that's close enough to it provided the guide dog is laying down. They're smart enough to know their right from their left, but they're not perfect beings.
On the topic of service animals and being on duty, a general rule is that if a person with a service animal is in public, that service animal is on duty. For guide dogs specifically, the dog will nearly always have a harness on. That should be the first indication it's on duty. Whether it's guiding or sitting at their feet, if the harness is on it's on duty. Please do not touch a guide dog on duty. The dog is the blind person's eyes. How would you react if someone came up and started touching your eyes without warning?