N7/4.2 Can't add lock screen widgets?
I have the same issue, N7 with 4.2 with an Exchange Corporate Account that forces a password/pin.

You are correct that it has to do with corporate account.  I removed my corporate account and was able to add widgets, even with the security still set to "password to unlock".  I also changed to Pin and Slide to unlock and all of them worked as well.

I then re-added my corporate account and the widgets that I added were gone and I was unable to add any others.

That said it's not a huge issue for me as the only Widgets I had the option of adding were Clock, Gmail Inbox, and Calendar.  Clock is already there and I don't want my Email/Calendar displayed without unlocking the tablet.