Never saw a brake with top ports on a standard factory contour sporter barrel do damage to the stock or the bedding.... But then again.... If you search the intrurdnet long enough, I suppose you can find some data to support that hypothesis.
Poll some of the custom rifle
smith's that are sponsors on this site, and I think you'll find it's not an issue.
Better yet, poll some of the custom stock builders and you'll get a more precise answer, but "no" is still "no".