Hello Jviola,
The UID in the new Domain will be based off the new Zone settings. The only way the UID will remain the same is if the user account is using the AD object from the original Domain and the UID is being created based on the AD objects SID.
Will the user have a new account in AD or is the user account coming from the original AD domain still? If this is express or autozone (or build from SID is selected) and the User object is from the new domain the UID will be based off the SID which will definitely be changed in the new Domain so it will be a new UID.
There are other options for setting the UID for provisioned users in the Zone properties and each will be reset in a domain/zone.
You can manually set the UID for the user to what it was on the old Domain/Zone or you can change the Folder / file membership to the new UID that is assigned using the "chown" command on that server.
Please let me know if I can clarify and of the above information, I will be happy to help.