I've run into the same issue, but I cannot get the update package to complete the CWM install. The phone is successfully rooted via SuperOneClick; other root apps such as Titanium, Wireless Tether and QuickBoot and are receiving su permissions and are fully functional.
ROM Manager 3.0.0.7 also has full su permission. I've flashed CWM several times, RM says that 2.5.1.2 is present. I can see the update.zip from my PC. Booting into recovery brings up the Samsung Recovery Utility with the blue text. I scroll down to reinstall packages, hit power to select, and the update package fails the whole-file verification signature test and aborts. I've tried about 5 times with the same result each time.
Any help appreciated, TIA.