The advantage of employing united fans, is that they rarely ask for time off midweek. They don't need a few days off because they're heading to Spain or Italy for a game.
Honestly, seems a crazy idea. Of all the people I've worked with over the years, the only ones I've even come close to having an issue with are Liverpool fans. We had three of them in the same department a decade or so back, and it was like smug central. Walk past their door and the clangers on speed were inside, busy chatting so much shit about other teams they arguably didn't do any actual work.
You have to mix with different people to get different perspectives. Like skills, ideas and points of view are different person to person, depending on who they are and what they've experienced. Our place decided to show the whole world that management 'cant be racist because look at me I hired this minority guy' a few years back, and the recruitment policy unofficially became very weighted against whites. But it was the same result, a few of those noobies are still there and are decent people, muck in and are pretty interesting people. A few left, and one guy was a bad egg and left within 6 months after being fully trained up, for a major competitor, claiming inequality. Management were baffled, until they were reminded that it was them that made it all about race in the first place. But the fact is that the decent people were still decent regardless of their ethnicity, they know how to get on and were open to give and take in a new environment. The bad egg moved on again from his next job, because he's a bad egg and has a different mindset, open to conflict, in fact actively looking for it, in the workplace.
I just love the fact now too that so many of the rags at our place are no longer football fans. A few drifted to other clubs a few years back, Chelsea, Bolton, Macc, even Stoke, before kicking it into touch completely as an act of self preservation. Then all of a sudden they're slightly interested again in footy when city lose. I ask if they've been to any games recently, and they sigh and walk away knowing that they're starting a battle without even bringing a butter knife to the fight.
Office harmony is important. But if you're forcing that via a recruitment process based on your own preconceptions, especially on a larger environment, then you're missing the point. It doesn't come from all having a shared interest, it comes from being responsible and open, without being a tit. It doesn't always work, but you do your bit, and when it doesn't work it's invariably because someone was a tit or just can't accept another point of view, such a Liverpool aren't the 'joint best' team of the last decade. Only have to look on here to see instances of some blues attacking other blues just because their panties are pinching too tight that morning or someone doesn't agree completely with their own point.