As for regular reports, BigT is correct. Normally mods will just take no action at all if they don’t think a report needs action and they will not reply to the reporter because, again, it takes an extra step in order to reply to a report. First you have to copy the email of the poster, you can’t just reply back to the report, because that just gets sent back to the SDMB email. Then you have to create a new email entirely and paste in the poster’s email and then create your own title, etc.
That all said, I have done that before and will sometimes if I have something to say. More often I will just come here and PM the poster using the PM system, though. It’s faster/easier than replying to a reported post.