ClockworkMod recovery we get from clockworkmod.com has some proprietary additions which blocks any app other than ROM Manager to access recovery. But If you want CyanDelta to auto flash latest nightly build, you need open source version of CWM.
Here is vanilla build of ClockworkMod recovery for Google Nexus S from CyanogenMod repo.
How to use
If you are downloading img file, you can use fastboot command to flash.
fastboot flash recovery recovery.img
Otherwise you can use zip file which can be flashed from any recovery.