Q:

Can app developers indicate folders to be excluded from Déjà Dup?

OS X‘s Time Machine backup system has an API that let application developers indicate that certain folders belonging to the application should be excluded from the user‘s backup. This is done through an extended attribute set on the directory in the file system.
With the mission statement “[…] [Déjà Dup] hides the complexity of doing backups […]” I kind of expect there to be such a thing. As an application’s developer should be well suited to know what folders are safe to exclude. But I cannot find any mention of it online.
Nudges in the right direction or to the right feature request would be appreciated.

A:

Déjà Dup will ignore any files in ~/.cache.  So if you're asking because you have cache files, put them in ~/.cache/program-name/.  See the XDG basedir spec for more information.
You could also forcibly add folders to the user's exclude-list key in the org.gnome.DejaDup gsettings schema.  That's not very user-friendly (that key is designed only for users to modify), but it's a last resort.

