So, let's say I already did KOTFE once on my sorc, and just want to get it over with on the BH...

Am I able to complete the first chapter of KOTFE as light-side, skip to Ossus, and still get him?

The short answer is, "No."

The longer answer is that every choice that you could make in the skipped content is made for you based solely on your faction (and for a handful of choices, on your class):

* Pubsiders choose light and save Vette.

* Impsiders choose dark and save Torian.

* Exception: Sith Warriors save Vette.

* Exception: Imperial Agents let SCORPIO merge with Iokath.

* Exception: Impsiders go light and save Kaliyo, Aric and Theron.

* Anomaly: SIth Inquisitors who begin KotFE without manually completing their class story are addressed as "Darth Imperius" at the beginning of KotFE.

The longer-still answer involves the above plus a discussion of "save points". The autocomplete function autocompletes everything you did since the last save point, even if you already did that something and chose differently.

Research indicates the following save points:

* Somewhere near the end of your class story.

* The beginning of KotFE.

* The end of Chapter IX of KotFE.

* The end of KotFE (er, might be the beginning of KotET).

* The end of KotET.

* The beginning of Inflection Point (intro mission for Ossus).

Conclusion: if you want Arcann alive on an Impsider, you have to finish KotET manually and then skip.