The iPad's storage is so limited and the transfer of data back and forth from it make it less ideal in a high volume workflow.
I do import photos on to my iPad when I have it with me shooting (which is most of the time), but only for looking at in down time, or quick edits and posts to FB or email. Then I import off the card to my main computer when I get home and periodically clear out the iPad to free up space.
The iPad OS only shows the embedded JPG in a raw photo, so it may not be the best for deciding what to delete.
Edited to add this relevant article from Terry White:
http://terrywhite.com/techblog/archives/7606