Lack of shared IP adresses doesn't act as counter-proof.
The only case where it could would be if the logged IP addresses for both accounts traced to locations divided by a significant distance.
Just FYI.

Accused:
brandt
raytheruler

The accused are suspected of:
Conducting Secret Diplomacy

Game number(s):
8412757

Comments:
Throughought the entire game, raytheruler has never taken a territory from brandt , despite the latter having multiple 1-troop territories neighboring with raytheruler 's ...