WCAG Conformance Statement
A WCAG 2.0 Conformance Statement is the official document which lists that all pages and processes of your website or mobile application fully conform to all success criteria at the level you claim conformance. E.g. most companies want to conform to WCAG 2.0 AA so they must also conform to Level A as well as AA. A WCAG Conformance Statement is an all or nothing document where all success criteria must be met and none can be failed.
A Section 508 VPAT is different in that it can list both the good and bad accessibility features and can be created even if the web page or app is not fully accessible.