• The -dbgsym Debian packages are automatically generated by the Debian packaging toolchain debhelper(7), or, dh_strip(1), specifically. (See dh_strip --automatic-dbgsym: "The default is to create debug symbol packages.") The created debug symbols are those .debug files.
• So, no, catkin_make is not involved here, as @gvdhoom pointed out.
However, debhelper(7) generates the debug symbols into .ddeb packages which are not supported by reprepro. The GitHub issue https://github.com/ros-infrastructure/buildfarm_deployment/issues/186 discusses several possible approaches to publish the .ddeb files into reprepro. Note that at the very end of the thread, the PR https://github.com/ros-infrastructure/reprepro-updater/pull/60 is mentioned as the final resolution of the issue.