is it ok to use my ipod, itouch or ipad while charging the batteries?

Yes.

I have an iPad and an iPod. I leave both plugged into a USB hub connected to my computer most of the time. I use both while sitting at my computer desk and when I leave and take one of them with me, I have ample battery life for an outing. I like to keep them both charged, and if driving somewhere for 15 or more minutes, plug them into the car outlet also.