I don't think there are any issues with having two (or more) together in groups regardless of sex. The only thing I've heard of is some minor aggression when adding a new one to a tank that has an established territory as they can get a little territorial. But nothing very serious at all. These guys have been together in my tank for almost 4 months. I even considered adding another just so I can see more of them. They don't interact much (except for mating and the occasional minor chase like the one in that video).I’ve been waiting on my LFS to get some in. I told him I wanted two. Then I got nervous that if they weren’t male/female, they might fight and kill each other. Still of the fence if it is worth the risk. I would hate to lose one or both, after waiting all this time to get them.
I believe there's a way to tell the sexes apart that you might be able to do at your LFS when they get some in stock. I ordered mine from Reefcleaners.org and John gave me a male and a female. If you went that route, you could ask. He did the same with my sexy shrimp.