This might be more of a server-related question, but let's discuss the keys first to make sure we understand each other:
a) Is this SSH2 public/private key pair supposed to be the SSH server key used to authenticate the SSH server to the client?
b) Is the SSH2 public/private key pair supposed to be a client key, used to authenticate an SSH/SFTP client (such as Rebex SFTP) to an SSH server?
I'm asking because at first, it looks like "a)" (server keys), where private part of the keypair is only kept at the server and the public part (or its fingerprint) is provided to clients in order to make it possible for them to verify that they are in fact connecting to the correct servers (they "authenticate the server"). On the other hand, "b)" (client keys) are used to authenticate clients to the server (instead of usual password-based authentication), their private parts are only kept at the client machines and their public parts are stored at the server (~/.ssh/authorized_keys in case of OpenSSH).