I am looking a Sun Atlas Cargo bike (similar to the Surly Big dummy). It a used frame and the back brake studs are tilting to one side a few degrees, one more than the other. They don't look bent but they were welded on crooked. I am good at setting up brakes but I have never encountered this. I would be installing XT VBrakes. Can they adjust to deal with this problem?

Are both the studs tilted to the same side, or are they just unevenly tilted for toe-in, or what?

Both are tilted to the leftside of the frame. The left stud is tilted extra. The tilt is away from the rim on the left and towards the rim on the right. Unfortunately no picture.

They might be ok, or the brakes might chatter or squeal - maybe just sometimes, under some conditions. They could be remounted, I suppose. But why buy problems, unless the bike is a particularly attractive deal for some reason?

Definitely not remounting the bosses. I could also try a regular linear pull brake instead of the XT parallel push brakes. Or better yet convert to a disc brake setup as this has those mounts too.

Disc brakes sound like a fine solution and a nice upgrade, especially for all-weather use.

Imperfect stud alignment is a non-issue for canti brakes (within reason). The critical issue is brake shoe to rim parallelism, and as long as the studs are close to inline, you'll adjust the shoes the same way as you normally do. The only time stud positioning becomes critical, is if you're mounting something that connects both like a brake booster. Of course, with imperfect stud placement, you'll have no choice about using shoes with a float system like convex/concave washers.