Craft 3 cannot find mysqldump command, console works
After a lot of digging I found an SO post which recommended updating the environment variable via PHP:

putenv("PATH={$_SERVER["PATH"]}:/usr/local/mysql/bin");


Adding that line into craft/config/general.php before the return statement did the trick for me. Craft does back up and Feed Me runs the feed successfully.

BUT: Is that a good solution?