Yes, it does! So here's how to tell if something does or doesn't effect plainswalkers:

things like [[doubling season]] specify when AN EFFECT would put one or more counters. As such, plainswalker etbs double counters, but not pluses, as an effect isn't putting the counters on, but rather your adding the counters as a cost.

Cards such as [[vorinclex, monstrous raider]] and [[all will be one]] specify when YOU would put one or more counters. As such, they don't care how they are addicted, as an effect, or a cost, just so long as your the player adding the counters.

Interestingly enough, vorinclex is a replacement effect, which will cause doubling season like effects to then take place, so having both out would give 4x counters.

So all will be one is pretty good for a superfriends deck, as it triggers off etb and off upticks.