Adobe isn't going to be monogomous towards Blink but they will continue supporting Mozilla's Gecko as well as WebKit too. Adobe's Vincent Hardy wrote that he feels Blink will "strengthen an already healthy browser competition." Adobe will contribute to Blink through their Edge Tools development, which is driven by the Chromium Embedded Framework. There will also be other contributions to open browsers for driving new features to the web.
More details can be found in this Adobe blog post.