That set-up may work great for a while, but will GREATLY reduce the lifespan of the LEDs. There needs to be a current limiting resistor in series with the LED to keep it from burning itself up.
Out of curiosity though, what's the rating (forward voltage) of the LED? I know a 12V fan will run at 9V and slightly under, but am curious what kind of voltage they're seeing due to the LED.
Thanks,
ATM
ShackMan