Yeah, I have a CAG Squad in Monster Hunter running. Like Darth says, it was created in the Japanese Niche Deals thread and thus is mostly filled with people from that thread/PSN community. I looked here for a Monster Hunter thread after creating it to mention it there, but I didn't see one so I didn't bother posting about it here. I check these sub-forums less unless there's a game I'm actively playing that has an active thread here.
It's still fairly active and I can invite people into the squad, but their invite system is a pain in the ass. Only the leader (me) can invite and I need to be in the same lobby as you to be able to invite. You can be in the middle of a mission, but I can't be in a mission. I also can't leave the lobby until you've accepted the invite.
We've got around 20 members in the squad currently and it's still fairly active. The best way to get in is to send me a friend request and mention CAG/Monster Hunter. Then anytime you see me on and not on Netflix, shoot me a message/lobby invite while you do your own thing in game and I can jump in to shoot you an invite.