No, the stock ArmA2 campaign "Harvest Red" only supports a maximum of 4 players in Co-Op. If you want to play campaigns in Co-Op with at least 5 players here are my sugestions (I'm assuming that you and your friends have ArmA2:CO or ArmA2+OA):
- Joint Operations, a campaign that uses BAF official DLC (British Units) and IMO it's the best user made campaign made for ArmA2 so far (at least regarding the ones that I tried so far) and it can be player with up to 8 players in Co-Op. This campaign can be downloaded here:
Joint Operations- Delta Force 1, a campaign that uses Lingor Island and Lingor units addons and can be played with up to 8 player in Co-op (if I'm not mistaken). This campaign is based on the old Delta Force games from Novalogic. This campaign can be downloaded here:
Delta Force 1- Delta Force 2, a campaign that uses no addons and can be player with up to 8 players in Co-op (if I'm not mistaken) and is somehow a follow up from the previous Delta 1 campaign. This campaign is based on the old Delta Force games from Novalogic. This campaign can be downloaded here:
Delta Force 2 - Ghost Recon: Island Thunder, a campaign that uses Lingor island and Lingor units addons and can be played with up to 9 players in co-op (if I'm not mistaken). Like the name says, this campaign is based on the Island Thunder addon for Ghost Recon 1. It can be downloaded here:
Ghost Recon: Island Thunder I hope this helps and keeps you and your friends "occupied" for a while