Is it possible for Google to detect app updates that have not been delivered through Play Store? I'm playing a game that is developed by a sub-division of Google. (Ingress/Niantic)

Usually new versions of this game pushed out through staged roll-outs, which means if you are not one of the lucky ones you have to wait a while to get the new version with sometimes cool new features.

Of course, the APK files for the new version could be found all over the internet on various sites. This naturally leads to two things:


There are APK files that are tempered with
Players get banned for using an unofficial version of the game.


As a curious player I want to have the new versions as soon as possible. To verify I'll have an valid build a downloaded the APK from the previous version, that I installed through Google Play, to my computer via adb.

$ adb pull /data/app/com.package.name
$ unzip -p com.package.name-1.apk META-INF/CERT.RSA | keytool -printcert | grep MD5


Which gives me:

MD5:  A7:E9:93:81:E9:F2:10:0E:48:39:AB:48:34:F3:93:67


Now to do the same with the APK for the new version that I downloaded somewhere from the internet and the MD5 of the certificate matches the one from the official older APK.

My question are now:


Is it safe to assume this is a valid APK that is not tempered with?
Is is possible for Google to detect that I installed the new version of the app not through the Play Store?
Could they somehow detect the unofficial update from within the app. For example through the Application Licensing service?
I used to play Ingress before, and I was able to update to newer versions using APKs uploaded by other players. I don't know if Google's verification process has changed, but as long as it's an official APK (i.e. not modified), it should be fine. 

Also, according to this Google+ thread, the verification process uses Google Play Services.