The command is documented here for ISE 1.3:
http://www.cisco.com/c/en/us/td/docs/security/ise/1-3/cli_ref_guide/b_ise_CLIReferenceGuide/b_ise_CLIReferenceGuide_chapter_0101.html#ID-1363-000006cf
It won't have any impact on a running system (meaning, it won't cause services to restart), it just adds the SSH host key for the SFTP server to ISE's key repository.