Interesting question. I haven't had much luck trying to find further information on this topic within the Community.
I take it that Google Adwords doesn't have what you're looking for? I'll try to do some digging on this and see if we have any experts that can give a hand......
There's a full list of APIs avaialble, documentation @ Using the Travel Partner v2.1 APIs | Hotel Ads | Google Developers
You will need to setup the OAuth properly, find how to do this @ OAuth Connections
I've never heard of Google Hotel Ads until now, but it looks like it should be doable - you just need to get the authentication setup done first.
Please post about your progress here, I'd be happy to help but see how you go first