The answer to your question is YES and NO.

Yes the "Case IDE Light" will still activate.
But NO it will not activate on any drive connected to the Extra IDE card.

Let me explain.
You say you want another IDE card for more IDE devices. Any IDE device you connect to this extra card will not activate the "Case - HD Light"; while the hard drive light is connected to the motherboard.

If you move the "Hard Drive LED" on the case , to the new IDE card, then the drives connected to the IDE card will activate the lED light.(The prior statement is assuming the NEW IDE Card has a connector for HD LRD activety - Usually these cards do have a connector for disk activety).
Also, now that you have moved the case HD LED light off the motherboard, ANY IDE devices , connected to the motherboard, will NOT illuminate the Case LED light.

Just remember,
whatever device the "Case HD LED" is connected to, i.e. Motherboard or extra IDE card, then the devices connected to it will activate the LED.

I hope I explained this well enough.
Let me know if you need furthur assistance.