This could technically be done, but it is not supported. See the link below which says the following under Unsupported Deployments:
"A "centralized" Cisco Unity Express model where a single Cisco Unity Express system provides voice mail to IP phones at more than one Cisco CME or Cisco SRST site."
http://www.cisco.com/en/US/docs/voice_ip_comm/unity_exp/design/design21/cuemodel.html
Hope this helps. If so, please rate the post.
Brandon