I just set up something similar. The key for the NEC is to not set the profile on the Mac. When you create a profile with Spectravision, it will create and store a profile in the OS. However, that profile is only a small part of what the NEC is doing to manage the color. You can create multiple profiles for your NEC (AdobeRGB and sRGB for example) but just switching the profile in the Mac's Displays preference pane won't adjust things correctly.
If you launch the spectraview software, and choose your setup there, it will automatically change the profile used by the OS to the correct one, and of course more importantly make all the changes in the the display itself where the NEC controls most of it's color.
Additionally the NEC version of the i1Display included seems to do a very poor job of calibrating other displays (not sure what they've done to it).. You probably won't be very happy with the results if you use it with something like i1Match to calibrate the iMac. I have my NEC next to a 30" ACD, and tried it ... didn't work too well.