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no such thing as pledgers anymore, that was just for the old kick starter / backing system TGC used before they released to steam, all users are the same and have the same rights now.
So yes you can release to steam and need no special rights or even mention GG at all - you still need to own or have rights to all media of course.
Releasing on steam requires you to sign a contract with them (steam) and pay $100 upfront, the full terms and process is explained in detail when you attempt to do so.