I'm pretty sure dim shield blocks antimatter-ed creatures...
Normally, Dim does NOT block Antimatter. Wings and Gravity Shield does.
When I played with Acsabi during Round 1 where we had a good connection, both me and Acsabi were seeing Antimattered Scorps BYPASSING his Dim Shields.
Moreover, if you play an Antimattered Scorpion deck versus any AI that drops Dims (Trainer included) you will see that they actually bypass the Dims.
However, in PvP, there is a desync bug where one player may see his scorpions bypassing the Dims and the other player does not. That has happened in this match.
The reason the WMs considered the bypassing Antimatter a bug instead of the blocked Antimatter is beyond my knowledge...
EDIT: But, in general, I have no problems to grant Team Light the victory or repeat the game or whatever (if the rest of Team Life agrees of course). However, it looks like this bug has to be discussed with the community as a whole because it involves two very powerful and overused cards which may cross each other's way more than once in the event (I am obviously talking about Antimatter and Dimensional Shield).