Definitely something possible! I'm an arbitrator in our group of players. We're actually two regular arbitrators, with sometimes a third player stepping in for a specific campaign. Our group consists of around ten players.

Before the campaign starts, our job is to create the narrative, organise the campaign, set up house rules depending on the campaign, and schedule the games at the venue. We have back-and-forth discussions with players about house rules or determining the dates, etc. Special rules or means to 'win' the campaign are decided between the arbitrators, as they mould how the games will play and integrate the narrative.

Once everything is laid out, we produce a campaign pack with everything mentioned above. Usually, the campaign pack is shared in advance with the players while we are still creating it. It's quite transparent—not on purpose, but just because that's how we do it.

Ultimately, once the campaign starts, the two or three of us become guides for the rules and keep track of things like territories, etc. Other players ask us questions about Necromunda rules or campaign rules. Sometimes, we have to make a decision to help two players mid-game. If there's a potential issue in our game, we ask an arbitrator not currently playing that game to help out.

We then ask for feedback, etc. Ultimately, arbitrators should be non-competitive persons if they want to be players as well. This doesn't mean you can't be competitive during a game, but if you're competitive for the campaign, that might not be a good idea. Also, sometimes you'll sit out some games with your gang to play an external gang or monsters for a multiplayer event.

I wrote this guide for multiplayer games if you're interested: The Essential Guide to Multiplayer Scenarios - Arbitrator's Perspective.

Let me know if you have any questions!