Hi ronaldo,
I do this all the time, I shoot raw on a Nikon d700, an Olympus e-p3 and occasionally on my old Nikon d40. For the first I use an ancient belkin 15 in 1 reader & the USB adaptor, it only works as the CF slot is the first slot on the reader. The other two take SD cards so I just use the SD reader.
Assuming your camera is supported you will be able to view the RAW photos in the photo app.
You can then import these photos into lightroom just as if you had plugged your camera in (I posted elsewhere that you need to take a photo on the iPad to get it to setup the folder structure for windows to see it). The intermediate step is great to delete the obvious duds. I personally import then leave them on the memory card til they're on the computer, so if I accidentally delete one on the iPad it's still on the card.
Following on, if you want to do some quick editing there are some great non destructive editing apps out there, I've got photogene, snap seed and plumped for photosmith fairly recently so now when I do portraits for people they can rate the photos they like and these stars are taken into the Lightroom import.