Right. But you're only controlling the camera with the tablet. The images are being stored on the camera and you're using the Live View feature to preview what you have. Yes, Helicon Remote works on Android. There isn't an iPad version yet. Brightness can be adjusted on all tablets. The Asus, don't know offhand of any others, has the IPS+ setting which gives an extra boost.
There are apps that will allow you to view post-capture. You can view from an attached card reader rather than using the onboard storage of the tablet. There again, an iPad could be problematic. Apple limits the amount of power that attached devices can draw. If the card reader needs to draw more than 20 mA (the Apple imposed limit) then it won't work. Android, don't know about Windows tabs, doesn't impose such a limit. Most apps (all but one) show you the embedded JPEG preview so not a lot of memory use to do that. Photo Mate Professional is the one that will actually decode the RAW files. I've tested it with D800 images and it does work, but is a tad slow. It shows you the JPEG in the thumbnail grid but if you open the full image in the editor, it decodes the entire RAW file. Nice thing about Photo Mate is that you can keyword, rate and colour code images, save those settings out to an .xmp file and LR or Bridge will pick those up when you transfer to your desktop. You can do it on individual files or in batch.