it's not just about what actually happens in the intended solution, but also what the player could think would happen. It doesn't matter if the result is "let the lemminas just walk there, it'll work out", if it doesn't look like that's what will happen. Remember - the player cannot tell, other than through trial and error... that such a setup is there.
OK, fair enough - I'll either reduce it to one teleporter/receiver and adjust the lemmina count such that it doesn't take too long for them to get through at the end of the level, or I'll simply spread the teleporters/receivers out so that it's clear how many there are.
that's still a hidden object, and if the player cannot see (or have to make an especially strong effort to see) what skills they contain, it's still unfair.
Another good point, it didn't occur to me that a player might go for the pickups anyway. That said, the process that you describe the player going through to find out what the pickups are is part of the fun of exploring a new level: I'd say this one isn't even that difficult to navigate around, what with its abundance of skills.
What if they were hidden such that the numbers weren't visible either (i.e. by only having single pickups)? That way, a player would have no reason to assume that they were even there until the talisman prompts them to explore, and thus they wouldn't waste time unnecessarily.
I'm reticent to change this one, simply because it's a bit of good clean fun. I
absolutely wouldn't mind playing a level with optional hidden pickups - in fact, I'd particularly enjoy playing such a level if it was otherwise fairly straightforward.
With that being said, I still want
Lemminas to be a pack that is completely fair, and I know what the likely result of a poll on this issue would be, so...
OK, I'll make the pickups visible.

I'd be interested to know your response to this, though. The idea of "exploration" levels is something I'd like to develop further, hence toying with the idea of a pack where every level has infinite skills and encourages player-led navigation. To some extent, hidden objects facilitate and enhance this idea, giving the player something to find within the level. Is there no way to do this fairly and enjoyably?