Yes, nnstreamer-openvino in Ubuntu PPA is built against openvino - 2019R3 and to use this instance of nnstreamer-openvino, you are recommended to unstaill your openvino and install openvino from nnstreamer PPA.

If cmake cannot find an openvino installation (probably you are trying "Approach 1"?), you may install openvino.pc (pkgconfig) to help build tools (cmake, meson/ninja) find them. For example, we have added openvino.pc for debian and rpm packaging at https://git.tizen.org/cgit/platform/upstream/dldt/ (/packaging/openvino.pc.in file is processed and packaged). You may edit the .pc.in file and install directly to /usr/lib/pkgconfig/