Only for valve games and retail CD key from third party listed in the following list : https://support.steampowered.com/kb_article.php?ref=7480-WUSF-3601
In the case of Rebellion, there will not be a retail version ( opening post )... only a digital download buy on Steam and a digital download pre-ordered on Stardock store... so, in this case, the following apply :
For games that incorporate Steamworks, users can purchase redemption codes from other vendors, and redeem these in the Steam client to add the title to their library.
Your digital download purchase on Amazon are simply game with Steam serial... in their description, you find something like "A Steam account is required for installation and online play"...
In some way, it is like Stardock sell serial to Steam, and Steam sell some of these serial to Amazon... Not sure that Steam contract will allow Stardock to sell directly serial to Amazon for a game who need to be used on Steam since it will cut them from their 30% share...
Well, like i wrote before, everything is possible... maybe Stardock have make a deal with steam, so that key from pre-order on Stardock store will work on Steam directly... i don't know, you don't know, nobody know... in fact, only Stardock know but they don'y inform their customer or potential customer... on the stardock store page for rebellion, it is always writen "Impulse::Reactor support for chat, friends, achievements and more." ( https://store.stardock.com/product/ESD-SDE-W011 )... if some people have not make a review article on the upcoming Rebellion, we will have never know about these Steam thing... not a very honest move to change one of the game feature without informing people who have pre-order the game, people who discover it by reading a external review article...
As car analogy are often used on these forum... you order Rebellion with features like :
and you end up with a Rebellion steam version with features like :
only useful for maybe 0.1% of the actual customer who build... sorry, play ... online