No, Google Wallet doesn't. When performing a tap & pay at a merchant NFC terminal using Google Wallet with your Android phone (running 4.4+), your Google Wallet Mastercard card is the card-account actually being used vis-a-vis transaction authorization. Then, later, Google will charge your card that you've configured to be your default-payment card. I do not know if Google is fully implementing Mastercard PayExpress spec, but they are implementing some of it at least. Thing is, because Google Wallet is HCE-based, and thus there's no secure element, they cannot permanently be storing the encryption keys needed to generate the cryptogram(s) and such that are part of a standard EMV transaction (Mastercard and/or the issuing banking of your Google Wallet Mastercard - Bancorp[1] would never allow permanently storing the encryption key w/out a secure element).

[1] https://support.google.com/wallet/answer/2676665?hl=en

Interesting. Does this mean that transaction data (what I bought, when I bought) is visible to Google, unlike Apple Pay (claimed)?

Yes, it is.

http://www.google.com/wallet/faq.html#tab=faq-security

I don't know, but I do know that Google Wallet has some kind of 'ghost' credit card number - that's the one that gets sent to the terminal, then presumably Google charges my actual card in the background somewhere.

no

Care to back that up with sources or a reference?