Yes, it is. Nemp checks the directory it is located in.

If it is "installed" in a subdirectory of "program files" (or "program files (x86)"), Nemp behaves as an installed program ans stores all data in the user directory.

If it is copied somewhere else, Nemp is portable and writes all data (settings, library, playlists, ...) into the directory Nemp\data.

If Nemp is located on an external harddrive along with your music collection, you don't need to worry that it won't work on another PC. Nemp will adjust the paths automatically if necessary.