Will the Season Pass that's available on the Origin store work with the Retail/GOG version of the game?

The origin option is considerably cheaper locally, by third actually.

Question is: does Origin let you download and install DLCs without getting the base game first? I don't know Origin, but for instance Steam doesn't allow you to do that.
Even if it allows you to do that, I don't think it will recognize your installation folder of the base game.
Here's a similar question to yours, it may be helpful:
http://www.gog.com/forum/the_witcher_3_wild_hunt/steam_dlc_when_bought_on_gog

I think the question here is if the code of season pass bought on Origin will be redeemable here in GOG too, like was with all other The Witcher previous games
In some regions, buy offers on GOG is much more expensive than pay the full price on Steam/Origin/Uplay, and some people has The Witcher 3 on GOG cause bought a physical retail disc and redeem the game here with the code that came together (Like i do, because it was more cheaper than Steam pre-purchase offer). For these sad guys, the only hope to play the Season Pass without buy all whole game again is if GOG accept the code from Origin (That will permit you to buy the Season Pass only, but i don't know if it will show on our account if the base game isn't there).