Which update are you talking about using,is it an RUU or an 'over the air' update?

The RUU will work but will return the phone to unrooted (albeit 2.2) stock. As far as I know the 'over the air' option should never be used on a rooted phone as it will cause all sorts of problems.

edited to remove potentially wrong info based on my lack of knowledge of CDMA.

 

With the OP using a CDMA handset they're limited to the ROMs they can use. I've made a rooted version of the new update which you can find over on XDA:

[ROM][CDMA][09/02/2011] Pre-Rooted Stock 2.2 ROM for USCC Users RC1 - xda-developers

Take a look if you want

 

"Over the air" would be an update downloaded to the phone via a wireless network. If your phone announces to you that an OS update is available, that's an OTA, and you do not want to accept it if you are rooted.

The US Cellular update you download onto your PC is the RUU (ROM Update Utility). You use this by connecting the phone to the PC (Windows only) and running the program. This will completely overwrite the software on your phone, unrooting you in the process. This is safe to use on a rooted phone, but I would expect it to wipe the phone as well, so back up any important data first.

 

Over the air is a part-update (not full release) delivered directly to te phone rather than download and installed via a PC. OTA will probably break things. If you run an RUU and run it from PC it will be fine, but will wipe your phone

 

Take a recovery backup (nandroid) before flashing, and if it doesn't work then you can simply restore from the nandroid backup and be back where you started.

Note: the one caveat is that I don't know what Eddy's put in here. If it's just the ROM then the above statement should be true. If there's a radio update in there as well then it is slightly riskier, as a nandroid can't undo that if it goes wrong.

If you are unsure, the RUU is the safest way to update, though you lose root in the process. scubab over in the main HTC Desire forum reports having used this on a rooted phone with no problems (like other posters here, I'm GSM so can't test this upgrade myself).