No, you can't do that. LR Mobile can work on photos imported from the iPad camera roll, or from photos synced over the cloud from LR desktop.
I bought a My Passport Wireless Pro last week. The main reason I bought it is to use it to backup of all my SD cards when I'm travelling. No body wants to loose pictures from Iceland or Africa...
On my iPad, I loaded the 3 following apps: LR Mobile, WD My Cloud and FileBrowser.
You need the WD My Cloud app to configure the My Passport Wireless Pro. With this app, you can not review your RAW files.
I'm just beginning to use the My Passport Wireless Pro but here what I've been able to do so far:
Load RAW files from a SD card to My Passport Wireless Pro
Preview RAW files with the FileBrowser app on iPad, "full screen"
Open selected RAW file in LR Mobile (using "Open With" option of FileBrowser)
Edited the RAW file with LR Mobile
Sync this picture in LR desktop (iMAC)
The RAW file has been transferred on the iMac, in LR Desktop Folder & LR Desktop Collection (All that automatically by LR sync)
From my iPad, with FileBrowser, I can even access all the files on the iMAC (via WIFI)
From my iPad, with FileBrowser, I can transfer any file from My Passport Wireless Pro to iMac and vis versa
So iPad / My Passport Wireless Pro / FileBrowser allow you to review your pictures taken in RAW on your iPad and to do a lot more.
LR Mobile is a plus if you want to edit your pictures when you are on the road and don't want to do it all over again once back home.
Hope this will help