They are in fact the same, yes you would be able to swap them over, how ever you would need to swap the internal components in order to retain your existing mileage. Also if the cluster you are planning to use, uses front mounted LED's you will have to wire those separately, if your original cluster did not have them.
I did an 04 S80 Executive cluster (black R cluster) in my 04 V70, but the XC90 cluster is an identical part.