I can't try it out yet, but my research on a solution for getting packets from the CC2531 sniffer to Wireshark for decryption decoding keeps turning up an open source custom firmware + Windows or Ubuntu client solution called ZBOSS Sniffer. It requires some initial setup in Wireshark, but apparently should do the trick. The only downside is that it seems it hasn't been updated since it was released in 2013.
If you have a Mac, there's also a Python based solution called ccsniffpiper here. The main advantage of this solution is that it works with the original TI firmware for the CC2531, and just creates a pipe that makes the packets available to Wireshark. I plan on trying this solution first when I receive my CC2531. I plan to try this solution if the new TI sniffer software doesn't do the trick.
I found reference to ccsniffpiper in a very informative PDF document explaining how to set up and use Wireshark up to do ZigBee sniffing.
EDIT - I should have just looked at the information on TI's download page for the new version of their SmartRF Packet Sniffer software. It states that the software includes "Dissectors for Wireshark" and that it "uses Wireshark for packet display and filtering". Further down the page, the CC2531 USB Dongle is listed as supported for ZigBee protocol sniffing. So I'll try this solution first!
