I swear I've mentioned it once somewhere, but I don't seem to find it. Anyway, I've tried it myself with some hex editing, it's been a while, and basically, when you assign the Attractor to a lemming in the Classic tribe, that lemming turns into a constant looping vanishing lemming (the same animation when a lemming burns in a fire jet trap). All lemmings around that messed up attractor will constantly be knocked out as if there's a constant bomb exploding as the place of the attractor. It's very weird.
Now, how about the opposite: would a Blocker skill work properly in any other tribe?
EDIT: Just tried it and Lemmings don't react to a blocker lemming in other tribes, they simply pass through it (for the only single time!). You can't assign another skill to that blocker in order to free it, and if you assign another permanent-kind skill, like the runner, the game crashes totally. So nope, the Blocker skill is really reserved for the classic tribe, the Attractor in the others.
EDIT: Here's an uploaded video showing the Attractor bug on the first level of the Classic tribe:
http://www.mediafire.com/download/7bx9k5k84a6s8ui/l2_000.avi