Disable power LED blinks during Vista hybrid sleep?

No you can't. The blinking is controlled by the motherboard, not control by the OS.

You can try to put some tape to cover the LED or unplug the LED light from the power supply though.

Well, to add theoretical hardware solutions: if the LED is too bright, adding a simple resistor will do the trick. A somewhat neater if more speculative hack would be to add a passive low-pass filter which is nothing but a resistor and a capacitor. If you get it right, it would turn your blinking LED into a pulsing LED which is maybe less distracting and might look better. However, LEDs don't have a linear response curve, so you should prepare for the payoff not looking quite as cool as you would have liked. Also, I won't be held responsible for anyone trying this and bricking their mainboard.