The Multipeer Connectivity Framework probably is probably based on a proprietary protocol as I have nowhere seen that it implements PAN. It's only similar to it. As you mention, the list of supported profiles contains PAN as well with the following note:
Depending on the Bluetooth accessory, you may experience slight
variations in profile functionality. These variations are governed by
the accessory manufacturer, not the iOS device.
So in theory PAN is supported as is, and you should be able to connect with an arbitrary device that supports this profile. I connected my Android phone to my iPhone with the Personal Hotspot on the iPhone and the Android could use the shared internet connection without any issues.
I found the Raspberry Pi Bluetooth iPhone Tethering tutorial that seems to describe exactly what you are trying to do. For future reference I copy the steps here:
Install the bluetooth packages
sudo aptitude install bluetooth bluez-utils bluez-compat
Pair the devices, this is the tricky part
pi@raspberrypi ~ $ hcitool scan
Scanning ...
18:34:51:55:B0:D8 Fanboy ][
pi@raspberrypi ~ $
pi@raspberrypi ~ $ grep KeyboardDisplay /usr/bin/bluez-simple-agent
capability = "KeyboardDisplay"
pi@raspberrypi ~ $ sudo perl -i -pe 's/KeyboardDisplay/DisplayYesNo/' /usr/bin/bluez-simple-agent
pi@raspberrypi ~ $ grep DisplayYesNo /usr/bin/bluez-simple-agent
capability = "DisplayYesNo"
pi@raspberrypi ~ $
pi@raspberrypi ~ $ sudo bluez-simple-agent hci0 18:34:51:55:B0:D8
RequestConfirmation (/org/bluez/18868/hci0/dev_18_34_51_55_B0_D8, 160178)
Confirm passkey (yes/no): yes
Release
New device (/org/bluez/18868/hci0/dev_18_34_51_55_B0_D8)
pi@raspberrypi ~ $
pi@raspberrypi ~ $ sudo bluez-test-device trusted 18:34:51:55:B0:D8 yes
Turn on the Personal Hotspot
pi@raspberrypi ~ $ echo "echo 'iface bnep0 inet dhcp' >> /etc/network/interfaces" | sudo sh
pi@raspberrypi ~
$ sudo pand -c 18:34:51:55:B0:D8 -role PANU --persist 30
Enjoy
pi@raspberrypi ~ $ ifconfig bnep0
bnep0 Link encap:Ethernet HWaddr e0:91:53:61:0f:74
inet addr:172.20.10.10 Bcast:172.20.10.15 Mask:255.255.255.240
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:14 errors:0 dropped:0 overruns:0 frame:0
TX packets:7 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:4426 (4.3 KiB) TX bytes:802 (802.0 B)
All credits go to http://www.wolfteck.com/ for providing these detailed instructions.