Generally speaking, questions about tools used exclusively for Drupal should be on-topic for Drupal Answers; for example, Drush is surely not a module, but questions about Drush are on-topic. If I cannot expect people using Drupal to answer questions about Drush, I don't know where else I should ask questions about Drush; for sure, I cannot ask to people using WordPress, or C#.
On Stack Overflow, questions about tools are accepted if the tools are normally used from developers. As far as I recall, tools that allow to upload files on a site are not considered developer tools; in the same way, a tool that would allow me to manage a Drupal site from my iPad would probably not be considered a developer tool, since that is a tool that Drupal site managers could use (without being required to know anything about developing).
Clearly, there are questions that suit more a support channel, if one exists. Contrary to questions about modules, where it is evident when something should be reported on the appropriate channel, for tools that is not so evident.
For example, if a module throws a warming or a fatal error, that should be reported on the project issue queue, since a warning means the code is doing something wrong, and modules are supposed not to throw warnings. For a tool, if the question is not about the reason the tool is crashing, the user could think something was not correctly set; it is not possible for the user saying if that is a bug or a misconfigured tool, especially for users who started using that tool.
It could happen that a Drupal tool is well known to be used from enough users, or it could happen the tool is used from a niche; that should not make any difference for us. Eventually, the difference would be that in one case the user would not get an answer, and stop asking questions about that tool.
The fact the tool is open-source or close-source should not make any difference, since in most of the cases the answer is not editing the tool code.