Yes you should be able to. I had to run a different update on my droid 2.2 because it was having service problems. I loaded another update.zip and it worked fine. Still works fine and has a lot better service.
Look at the 3rd link in my signature. You should be able to use RSD Lite to flash the SPRecovery file on your phone and then install pretty much whatever rom you want from there. Some people have said they have issues being on 2.2 and flashing SPrecovery so the next step would be to go back to a previous android OS like the ese81 sbf file that is rooted. From there you can install a 2.2 rom.