I just tried it for the first time, and it took some troubleshooting.
First off, I'm using PPPoE, and eth1 doesn't have an IP address associated with it -- ppp0 does. Also, the username and password didn't seem to be being passed in properly, since I got prompted for both when I ran the command manually --
/sbin/e-smith/dynamic-dns/easydns restart
I just ended up editing the template file to hardcode my settings --
/etc/e-smith/templates/etc/easydns.conf/10easydns
gets edited to look like this --
service-type=easydns
user=youreasydnsusername:yourpassword
host=host.yourdomain.com
mx=mail.yourdomain.com&backmx=YES
interface=ppp0
cache-file=/tmp/ez-ipupdate.cache
Lastly, I'm still getting the "malformed cache file" message, but it seems to be working.