The quick and dirty answer to that is: YES. Obviously, with soldiers standing guard there night and day and at full alert, a busload full of tourists likely won't be anything near the first casualty if something does go down. The North and South Koreans are trying to kill each other, not some random, fannypack-wearing families looking for a nice outing. Besides, tours come and go one at a time, are led by official military personnel (usually American), and you will be kept very in line, as in "don't take two more steps to your left" and "no cameras allowed out once you step over this line."
Secondly, the bullets that just flew were between two guard towers; the guard towers are fairly distant from any tourist activity, although you can see them through binoculars or a zoom lens. Heck, you can see North Korea proper that way too. That's why the DMZ is called one of the most dangerous tourist traps on the planet.
There is only one way that the DMZ could be dangerous to tourists, and that's when the tourists themselves step out of line and do something stupid. That's how to get shot for sure. Take for instance the South Korean woman tourist who, while visiting a resort that is technically in North Korea but allowed visitors (most of the time), went around a fence and into a North Korean military area before dawn and didn't stop when ordered to. She got shot. Don't do that.
This is one of the few times when you'll hear us say this: a bus tour can be your friend.