I don't see why they couldn't. All the game cares about is power and traction rating, not where it comes from. Ofc if they are modelled as separate units then people could still use them in game without a parent locomotive. Alternatively they could be made as 2-unit pairs (like A/B sets).

Tbh I thought there were already some in the workshop but I can't find any (searching for slug). Only mention is this mod that a slug is in the works:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2843717509

Originally posted by Blast Hardcheese:

I only just discovered what these are today: https://en.wikipedia.org/wiki/Slug_(railroad) They're like B units without a prime mover that derive their electrical power from the A unit. They'd have zero power and only a tractive effort rating. Could these be modeled in game?

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2534396600
this is the closest thing on the workshop i know, but it has a prime mover
I don't believe the effects of more prime movers can be simulated properly, it would just be an extra engine like this one