If I back Divinity: Original Sin 2 and I want to get my copy on GOG, will I still have Alpha/Beta access?
You'll definitely be able to access the Alpha/Beta through Steam (and hopefully through GOG too, but we're working on that at the moment and it’s not 100% certain). However, the Alpha/Beta access that you choose won't affect which version of the game you get when it ships. So, you can access the Alpha/Beta through Steam and then get the final game on GOG.com if you want.
https://www.kickstarter.com/project...nal-sin-2/description#project_faq_146053