Finlay offered Ves a means to contact him or the faction standing behind him. Of course, he didn't exchange comm addresses or anything else that could be traced back to his real identity.
Instead, Finlay passed a so-called Shadow Address to Ves. This was a unique identifying code that Ves could use to send a message to Finlay via the Shadow Courier network.
People made use of Shadow Addresses in case they didn't want their real identities to be associated with their shady dealings.
For example, if a Sentinel noble requested the shipment of a batch of nuclear missiles, then he wouldn't tell the seller to ship the batch to 'Lady Miralix of House Laterna at Felixia I' or something!