So I get that Luke Skywalker (Jedi Knight) Operative's command cards and Luke Skywalker (Hero of the Rebellion) Commander command cards are interchangeable as per the news release (" Meanwhile, three command cards that can be used alongside the Luke Skywalker command cards from the Star Wars : Legion Core Set give you the freedom to shape exactly how you use this powerful operative in battle. "). Are the figures interchangeable as well. I was looking through the rules and I could not find a ruling that clarified this. Basically, what I am asking is: Can I use the Luke Skywalker (Jedi Knight) mini as my commander while using the Luke Skywalker (Hero of the Rebellion) card?

As you already said, there is no hard rule for what figures to use. So it's completely up to the players and I'd say if you make it clear to your opponent, what your model represents it's fine 99% of the time. I'd pack the "original" Luke as a backup for Tournaments and ask the organisers before the event though.

Seems as though you can. From the announcement article:

"Featuring new miniatures and command cards interchangeable with the Commander units found in the Star Wars : Legion Core Set , these units give you new ways to unleash the power of the Force on your opponents!"

Its the card that defines which Luke (or Vader) you are playing in a list, not the mini. You can only play 1 unique unit at a time, so there shouldn't be confusion unless your opponent is easily confused!!! Even the Adepticon Vader is legal for comp play from what I understand, so Vader will have 3 official figures to choose from.