The plugin source code is GPL, however use of Google Services through the plugin is governed by Google’s Terms of Service and Privacy Policy. For products and services that can be used with the Google Publisher Plugin, such as AdSense, additional Terms of Service may also apply.
That has nothing to do with the plugin itself. A plugin can be GPL and allow users to connect to services that are not GPL. This is quite permissible.
If you still feel that this is a violation of the plugin submission guidelines, then please contact plugins [at] wordpress [dot] org with all of the relevant details. However, I suspect that this will come under the acceptable “Serviceware” definition.