Q about registering games from Steam/GOG

Hi,

This has probably been asked before but a search didn't find anything recent.

Can games bought & registered on Steam or GOG be registered on my Stardock account, or don't they need to be? How do I get support if needed or do I rely on Steam/GOG for that? Also, if I buy DLC's here, can they be used on my standalone GOG games or only on Steam?

I got the GOG versions on special because I live in Australia with very unreliable internet. I was offline over a week recently. So I can't play Steam games! (I also just bought Object Desktop, though that's not relevant I suppose).

Basically, I'm just trying to simplify things. 

I've bought these games on Steam:

Ashes of the Singularity: Escalation + All DLC's

Fallen Enchantress & Legendary Hero's with DLC's

Galactic Civilizations III + Crusade

Offworld Trading Company + Almanac

Sins of a Solar Empire: Rebellion

Sorcerer Kings: Rivals

The Political Machine 2016

The Corporate Machine

I also have via GOG:

Star Control: The Kessari Quadrant

Fallen Enchantress & Legendary Hero's (no DLC's)

Sins of a Solar Empire: Rebellion Ultimate Edition

 

Thanks in advance for any information.