Please refer to the Documentation tab for OpenDacs API for the matrix.
It does not mention which versions of DACS server it is compatible with.
However, if you refer to the release notes (on the same Documentation page) of the OpenDacs version 8.0.0.L1 its Software Requirements includes 'DACS 6.6 or higher'
There is no compatibility matrix document between a specific version of OpenDACS API and a version of the DACS component or daemon. As far as I know, there is no breaking change in the DACS library used by OpenDACS API, and I believe that it still works with DACS Daemon 7.x because it requires DACS 6.6 or higher like Umer said. The main purpose of this release is to support the new version of RFA.