FedConnect and SAM.gov (SAM) are separate entities. Both are websites that agencies use to post opportunities, however SAM is run by the federal government while FedConnect is run by a private company. Agencies can choose whether or not to post opportunities to SAM, FedConnect, or to use both. Additionally, agencies can also choose to post some information on SAM for an opportunity, but then prefer to receive bids and responses via FedConnect.
FedConnect also contains a built-in Message Center that allows agencies and vendors to communicate with each other about opportunity postings. All communication via the Message Center is secure, recorded, and auditable.