(I'm Boxer's developer.)
Boxer will import and run most of GOG's DOSBox releases, though there are some that the current version (1.2.1) will not import correctly at the moment:
Alien Breed Tower Assault, which seems to affect the Mac port of DOSBox too.
As a general note for everyone: If you do encounter problems getting a GOG release to run in Boxer, please
let me know directly via the Send Feedback link in Boxer itself, as I don’t read the individual game forums here on GOG.
If you let me know personally about the issue, then I can make an effort to fix the problem in the next release of Boxer; if you work around it but don't let me know, everyone else will have to keep working around it in future too, and that would suck.