Can the Samsung Galaxy Tab be used as a wifi-hotspot?
The Galaxy Tab comes with Android version 2.2 (Froyo), this version of the Android OS comes with the ability to work as a WiFi hotspot for up to 5 devices built in. This lets you share your Tab's 3G connection out to other devices over Wifi.

I've tethered wifi only devices like my Kindle 3, and a wifi Skype phone to my Galaxy S's wireless hotspot in this way and connected them to the internet with no problem, so I can't see any reason you'd have trouble doing that between a 3G Galaxy Tab and a Wifi iPad.

(it is possible for your phone company to block this facility, to date I think Verizon in the US are the only company to block it)