Really, there shouldn't be any situation where the dehydrated script produces no output at all, which is what makes me wonder if it's actually running at all. Hence the request for the output of "which dehydrated", as it would show where it's trying to run from.
If, for example, your PATH were completely bizarre, and looked to /etc/cron.daily/ before it looked to /usr/bin/, it would have that effect. Or if you were in /etc/cron.daily/, and instead of typing "dehydrated -c", you typed "./dehydrated -c", that would explain it. Or if you were in /etc/cron.daily/ and your PATH included "." (which it probably never should at all, and certainly never should as root), that would explain it. But all of these sound pretty far-fetched.