I want to test some apps on Nexus S devices, can I access the devices remote or get some emulator image for it?
for the GALAXY Tab, I could get it at http://innovator.samsungmobile.com/galaxyTab.do , but seems neither Samsung nor Google provides the actual info on Nexus S
The Nexus S is pure Android. You shouldn't need a special emulator for it, just use the standard emulator with SDK set to 2.3. You can get all the details you need from the tech specs.
Depending on what your app cares about, you probably just need to set the screen size appropriately: 4.0" WVGA (480x800)