We've been using the Moto G here for a few weeks now. Basically since the July 28th event in NYC. We do have a Pioneer head unit in our car and have been using the Moto G with it, without any issue. But it appears we are in the minority here. It looks like many others are having issues with it connecting. Google has taken note and is working on a fix. According to the post, it appears that when connected to the Moto G, Android Auto fails to start.
"Android Auto doesn't start on the Moto G. We're working with Motorola on a solution."
We are not the only ones that haven't had any issues with the Moto G and Android Auto either. So it appears to only be a few people. It's hard to say who it works with and who it doesn't. As there hasn't been an update just yet for the Moto G 2015. In fact, we just did a factory reset on the Moto G and plugged it in, and it worked just fine (although it took a bit to download updates for Google Play Services, Maps and Google Now. That's likely due to it being rush hour and on AT&T's network). So we're not really sure what the issue is, seeing as it's only some users and not all. Even Android Central isn't having issues with their Moto G and Android Auto.
While it doesn't work for some, it's still good to know that the folks over at Google are aware and they are working on a fix along with Motorola. Definitely a good thing. Let's cross our fingers that when the Moto X Play, and Moto X Style/Pure work when they are available. Now because it's a known issue, that does not mean that it's going to be fixed right away. In fact there are still known issues about voice search on the Galaxy S4 and Galaxy S5. So it could take some time. However, as usual, we'll be sure to keep everyone up to date with what's going on here with the Moto G 2015 and Android Auto.