I got frustrated with the lack of support for wireshark with JN51xx sniffers, so I wrote:
a) A command line sniffer server, available here: https://github.com/Codemonkey1973/JN51xx-802.15.4-Sniffer-Server
Use this command line utility with an eval board or module programmed with the NXP sniffer binary provided in the SDK's. It will then send the received 802.15.4 packets encapsulated inside a UDP message to the IP address of your choice (127.0.0.1 by default).
b) Added support for the sniffer server packet encapsulation format to Wireshark. Any of the automated builds created after 1st Jan 2018 contain built in support for dissecting the messages from the command line sniffer server above.
On windows you can either direct the UDP packets to your usual network interface, or find a guide on how to install the loopback adapter and sniff the packets on that at 127.0.0.1 (you will probably have to install npcap library instead of the usual pcap library if you want to do this.
Hope this is useful to someone!