The Debian packaging standard has rules on acceptable filenames for files destined to cron.d. Enabling these with a flag would be better than the current solution.
When checking files in a package's debian/ directory, filenames should only match the (\S+\.)?cron.d as opposed to the other names currently accepted. In addition the error for this should probably point the user at the above link.
I suspect other packaging systems have their own standards, so need to investigate those first.