Why are you asking? Did you see a post about dents? I think it depends on a lot of factors. Dents to someone might be dings to another. In other words, all dents are not created equal. Is the dent large or small? Is the dent a rounded affair or is there a "crease" in the metal? Is this a super high end SLX with quadruple butting and super thin tubing?
Straight gauge cromo could probably be bent in half and still be OK to ride. I'm exaggerating to make a point.
Personally I would never buy a vintage bike with a dent in the tubing, simply because unless I'm planning on repainting it, it would drive me crazy. If I did buy it, the size, location of the dent, etc. would dictate whether I would have it rolled out or just filled and painted.
I bought a Raleigh once because the saddle on it was worth more than what I paid. I put a different saddle on it and flipped it. The buyer was told that there was a small dent on the top tube and he didn't care a whit. He said it would have more next week because he wasn't particularly careful when locking his bikes up.
Bikes don't typically asplode in my experience, but when or if they do, there is surely a good reason for it.