It makes a lot of sense that Android ad SDKs will use Android\'s the new advertiser id.
It seems that you can only get the id by using the google services sdk, as me
MoPub and a few other big players are not including GPS into their SDKs. From MoPub's help page:
the MoPub SDK does not require Google Play Services. If you have it installed, we will automatically use the new Google Advertising ID. If you do NOT install Google Play Services, we will continue to pass the old Android ID. Note that all publishers need to use GPS in their app by August 1 to prevent their apps from being rejected by the Google Play Store
Check this link for a lot more detail:
http://help.mopub.com/customer/portal/articles/1523610-google-advertising-id-faqs
Hope this helps.