Can anyone confirm whether patch 7 is cumulative or not?
Currently I've got HP ALM SP2 (Patch 1 - 4). Should I apply patch 6 and then patch 7 or can I directly apply Patch 7?
Yes the patch 7 is cumulative. See the documentation for Patch 7. There is not exactly written that it is cumulative but there is written fixed defects for all patches before so I think it is cumulative as all other patches.