Those are cool tables - but is pine a mandatory choice? It will take a lot of surface finish (maybe use the polyurethane floor stuff?) to make something the staff can keep clean. As a complete contrast in everything from cost to color, mid-moisture jatoba provides a very fine, very hard, finish that won't be affected by beer spillage and won't warp much even if the beer tent leaks.

The problem with any kind of clamps other than plug in dowels is that something juts out - and staff will break them while customers will snag themselves on them. Drilling holes (and maybe lining them with metal) is attractive because the staff can put the dowels in only when needed, but (a) they will lose some of them; and (b) there is little lateral strength so when idiots dance on the tables while others push and cheer, something will break or crack.

I've never seen tables done this way, but you might be able to finesse most of the strength and safety concerns by making 2" or wider "finger" joints on each table. Make them about 1" deep and lateral forces will cause the tables to separate but won't break anything; an uneven floor will produce only minor irregularities in the long table, nobody is going to get hurt on the ends of the fingers; and most of the warpage problem goes away too. (and, in ten years, you can trim off the damaged ends and cut new fingers).