Exposing UnityEditor members via Reflection. Is it legal?

After a while inspecting Unity3D's assemblies, I've found some useful stuff I'd like to expose to use on my own tools. In this case I was looking into ProjectWindowUtil, which has some really useful methods I'd like to use.

On Unite 2012's Advanced Editor Scripting by @VoxelBoy, he states something like despite decompiling it's in fact against the EULA, he heard an Unity3D engineer saying that this is stupid, cause they are always telling us developers to do so. Correct me if I'm putting the wrong words in Yilmaz's mouth.

In case I want to create a tool that reflects some internals, in order to ease use of my own tool (i.e. no bad intentions here), and want to get the chance to submit it to the Asset Store, would that prevent me from getting my tool uploaded? In case it does, will it prevent me too from open-sourcing my tool, from a legal point of view?