I am not sure this is a good idea, since the cache is used for fast access.
A network drive is slower to access than normal media.
Of course how slow/fast depends on what device it is and what interface it uses to connect to the network (USB/ethernet etc...)
On top of that I am not sure if this will be a good idea from an amount of concurrent users perspective.
Maybe you should block Spotify and tell people to use their phones' mobile network data plans or local music files?
Edit: To actually answer you question instead of questioning it, Spotify supports caching on network drives I just found out. I haven't tried it, but it should be possible.
Maybe you should try with a simple thumb drive or HDD and see if it works optimally?