What They Saw
This set of genes seems to be homologous to A. vinelandii's hoxZMLOQRTV string, making the whole operon very similar in both organisms.
As in previous studies, HupZ (and its analog, HoxZ) seems to be an electron carrier in the membrane, possibly a cytochrome. When they knocked it out, they observed similar results to 070: hydrogenase could oxidize hydrogen with methylene blue as an electron acceptor, but not with oxygen, so HupZ seems to be part of the transport chain to oxygen.
Based on comparison with homologs in other organisms, HupM may help the hydrogenase attach to the membrane, or with processing the subunits. It's unclear. The other genes may be involved in processing or metal stuff. HupR may be another electron-carrying protein. Further study is required.