Hi,
I think what you are asking is whether DUCS should be installed on each Domino server or only the Unity partner Domino server.
If I've understood your question correctly, this link should answer it: http://cisco.com/en/US/products/sw/voicesw/ps2237/products_installation_guide_chapter09186a0080441386.html
Specifically, this excerpt, I think, answers your question: "Step 6 Install csServer, the server component of DUC for Cisco:
?On each Domino server that will home Cisco Unity subscribers.
?On the Domino server on which you created the Lotus Notes mail file in Step 2. "
According to babelfish, "annuaire" is "directory". That same link covers directory and other required component set up from Domino's perspective.
I hope this helps.