Hello there!
I haven't seen a simple clarification anywhere where the Separatists / Republic fall into the light/dark spectrum. Whenever I watch some battle reports online, it is assumed that Separatists are Dark Side and Republic Light Side. However, the rules reference on page 5 says:
The Galactic Empire is aligned with the Dark Side, and its units can equip “Dark Side only” upgrade cards, while the Rebel Alliance is aligned with the Light Side.
Separatists/Republic aren't mentioned at all. Has this been decided anywhere or is it assumed to be like I said?
On the same note, what about "Imperial only"? I'm asking this because I just watched a Battle Report in which the Separatist player used "Imperial only" cards (also implying that the Republic could use "Rebel only"). I presume that's a mistake?