The devices having Amazon app store don't have Google Play. Similarly Google play devices don't have Amazon app store ( and its not available on Google play to download, though one would grab it from its website but by default, Android devices tend to warn for apps from Unknown sources. So kind of neglible probablity of people having Google Play devices to have Amazon app store). The Ads in both kind of devices need to be different as the Ads of Games/ Apps download in AdMob should be of Amazon app store in Kindle devices and of Google play in other Android devices. This feature AdMob allows.
But the devices having Samsung App store(if its Android) will have Google play. So the Ads can be the same. Similarily for GetJar.
Though I dont know devices having SlideMe, GetJar, Yandex, Soc.io, etc as the only available app store. They must be having Google Play ( then only Google gives OEM's, Android OS for free, I guess)
I dont think, this will break AdMob's TOS unless you are showing the Ad placement as same as in the Google play version of your app.
Would be glad to have more information on this. But don't know if it is the right forums for this.
Best,
Kunal