So, according to the "Guidelines For Using Apple Trademarks And Copyrights":
Compatibility: Developers may use Apple, Macintosh, iMac, or any other Apple word mark (but not the Apple Logo or other Apple-owned graphic symbol/logo) in a referential phrase on packaging or promotional/advertising materials to describe that the third party product is compatible with the referenced Apple product or technology, provided they comply with the following requirements.
a. The Apple word mark is not part of the product name.
b. The Apple word mark is used in a referential phrase such as “runs on,” “for use with,” “for,” or “compatible with.”
c. The Apple word mark appears less prominent than the product name.
d. The product is in fact compatible with, or otherwise works with, the referenced Apple product.
e. The reference to Apple does not create a sense of endorsement, sponsorship, or false association with Apple or Apple products or services.
f. The use does not show Apple or its products in a false or derogatory light.
I'm no lawyer, but it sounds like the answer to my question is "No, you may not use the Game Center logo -- you can only reference the functionality in writing".
Am I reading it correctly, though? I have no idea, really.
I've contacted Support, but I'd welcome more input here while I wait for a response.