It depends on what you mean by “Google Fonts”. As fonts, they do not depend on CSS3, or CSS at all; you can download them and install them and use them. As a technique of using “web fonts” or “downloadable fonts”, they use the
@font-face declaration defined in CSS Fonts Module Level 3, which is commonly regarded as part of CSS3, which is as such just a vague collective name for various CSS specifications and drafts (more of a slogan than a technical term). This applies whether you use them as hosted by Google servers or on your own server (after having downloaded and processed the font files) or as shipped as part of an application.
Thus, the use of Google Fonts as hosted by Google versus the use of fonts (those from Google or any other fonts) on your own server or as part of an application package is not a matter of choosing between CSS3 and something else. There is no “something else” in this case.