Hi Matthew,
The UC500 series products are managed under the Small business BU.
Forum here :
https://supportforums.cisco.com/community/netpro/small-business/voiceandconferencing/sbcs-uc500
The current version of CUCME on the UC500 is 8.1
I think it's reasonable to state Cisco have a fairly well featured and robust SIP implementation, however I agree that this product is missing from the CCO software advisor tool. If you're looking for a particular feature I'd recommend posting on the UC500 forum and see if somebody picks it up.
Adam