Google Play Games without Google Plus
No, it is not possible to use Google Play Games without a Google+ account because much of Google Play Games is social and so it makes sense for it to integrate it with Google+. But if you don't want to use the social side of Google+ but still use Google Play Games, you could create a Google+ account and disable all the social features, make every aspect of your profile private and also disable all social options in Google Play Games too.