He worked with/for Edison the nature of the actual relationship seems to vary with source some. Regardless of anything else due to some known timelines he did not work directly with Edison for more than 4 years, and very likely it was far less time than that even.
I did understand them to be respectful rivals , they also both had very divergent ideas to answer several problems.
I think Nicola's work was equally as important as Edison's to be honest.
It almost seemed like he a instinct not only for the electricity but for magnetic fields and well there's a few theories in there that have still yet to be proven one way or the other.
It's thought several 'top secret' and major breakthroughs were lost in his big lab fire, but there is really no solid evidence one way or the other.
I looked over the wiki entry on him several years ago, at the time it was relatively accurate. There are a lot of things that are blurry about Tesla and it will probably always be that way.