Before you return your Mac Mini you might want to try a miniDisplayPort to DisplayPort cable.
I checked the Product Specifications for the P221W and it has a DisplayPort Input. http://www.necdisplay.com/p/desktop-monitors/p221w-bk-sv?type=support
The warnings from NEC about the use of SpectraView II with OS 10.7.5 and OS 10.8 all deal with cables that output to a DVI connection.
I had the same concern when looking into using the NEC PA271W with the Mac Mini or the MacBook Pro Retina 15".
The answer I got from NEC was to use a "miniDisplayPort to DisplayPort cable to the PA271W"
The Video Output for both the Mac Mini and the 15" MacBook Pro Retina is Native Mini DisplayPort output.
What I did not know is that the Thunderbolt port is also a Mini DisplayPort.
It is my understanding that all Thunderbolt ports (at least on Macs) can act as Mini DisplayPorts - Mini DisplayPorts can only be Mini DisplayPorts.