Is it possible to have two separate versions (release and debug) of SciDB 14.12 installed on the same machine? That is, will the instructions for the following page work for release and debug of 14.12?
Technically it is possible, but not using the same way pointed out in the URL you provided.
That URL talked about having two different versions of SciDB (e.g. the example used was 13.3 and 13.6), not two different installations with the same version.
The best way to do what you want is to do what’s called ‘local development’ in the build instructions manual, which may be downloaded by visiting viewtopic.php?f=16&t=1596 and selecting the latest release. In particular, “run.py setup -h” shows that it respects the SCIDB_BUILD_TYPE environmental variable, and “run.py -h” shows that it respects the SCIDB_INSTALL_PATH environmental variable. So you may build from the same source twice (once in Debug build and once in Release build), and install to different paths.