I did find this on the Cumulus MX site...
The LOOP2 packet is supported on the VP2 with firmware version 1.90 or later, and on the Vue. If you have a Vantage Pro (i.e. the original 'VP1'), or a VP2 with pre-1.90 firmware, or if you are using Virtual VP, none of these support the LOOP2 packet. In these cases, you should edit cumulus.ini and add a line to the [Station] section:
UseDavisLoop2=0
Not sure how this will help with connecting VVP to Weewx on the RPI, I have Cumulus currently and seemingly connected fine to VVP with the IP option.
I know my RPI rig running Weewx plugged directly into the logger runs great so Weewx can handle the Davis data stream through a serial connection. it's getting it to work over ethernet that is eluding me for now. If VVP was the culprate, wouldn't I have similar issues connecting to Weatherlink and Cumulus as well??