You can definitely take a guest to the loft with OWS or OWE. As far as I know, the only thing you can't do there, is use the area reserved for Lufthansa super-elites.

At BRU, you get proper Finnair-styled thick boarding pass. They look nicer than the bland ones at HEL initially, but they also lose their ink much faster. If you intend to keep it as souvenir, you should probably tape it after the flight.