"614.12. Some replacement effects modify how a permanent enters the battlefield. (See rules 614.1c–d.) Such effects may come from the permanent itself if they affect only that permanent (as opposed to a general subset of permanents that includes it). They may also come from other sources. To determine which replacement effects apply and how they apply, check the characteristics of the permanent as it would exist on the battlefield,…"

I've been told that this mean that a Scarwood Treefolk ability affects itself, ie, it's put onto the battlefield tapped while a Orb of Dreams doesnt affect itself. Correct?

I had trouble understanding it from the wording quoted. Is the phrase between ( ) supposed to discard the rest of the rule when the ability affects sets of permanents instead of a single one?

You understand correctly.

Scarwood Treefolk talks about itself only, so it will enter the battlefield tapped.

Orb of Dreams talks about a set of permanents, so it won't affect its own entering the battlefield. It will enter the battlefield untapped.

Daniel Kitachewsky
L3, Paris, France
Rules Netrep