Thanks to the help of Vivikain I was able to test what happens when this mod is used in Multiplayer. The results were interesting, to say the least.
The biggest issue with a second player joining is that whomever doesn't have control of a character has a completely black screen upon any map being loaded. Chat is basically the only thing that works properly. The way we found around this was to switch control of the character (even if temporarily) after loading the map; for some reason this makes everything visible.
When the map is loaded for the off-player, their camera position (which is black) is set far far away from wherever the player ended up. Luckily double clicking the character portrait fixes the positioning (and the control switching fixes the visuals).
The problem, however, is that the off-player has no skill bar if they're assigned control of the character. Like in this picture-
This also means that they can't use any skills, at least until the map is switched/reloaded with them as the on-character.