Yes it's probably how it's designed in the addon. May have to ask Wolv to be sure. /nsp is a directory that was made for the playtests, i may be wrong but once ns gets released on the "my games" list of steam, it will probably use the /ns directory again (or once its out of beta).
In the meantime i have copied my entire /nsp folder to a /ns folder and i run my map tests from there

So i don't need to copy my maps each time i compile, and i can have another keyboard setup (binds/scripts for cheats, dev commands like gl_wireframe, spectator arrow keys to take screenshots (mouse don't work to turn around), all the stuff i don't need on the ns install i
play with).
If you really want i guess you could make a .bat file wich copy the .bsp from /ns/maps into /nsp/maps and execute it after hlrad.exe in the build programs execution sequence, so it's automatic.
Hope i make sense, i just woke up