These are some of the casualty models for my Imperial Guard.
These models are from Pig IronPig Iron Casualty Models
Although not exactly the same wargear as your IG trooper from GW, the fact that they are casualities means they could be local IG, PDF or some other person. Scale wise they fit in nicely and do not look out of place, and although they are clearly non GW they still fit in the universe. Their weapons and gear could easily be IG or PDF and in fact I think they look a little like drop troopers.
They make great objective markers and add a bit of spice to the battlefield, which is why I have painted mine up to look different to my guardsmen (all several hundred of whom have a common theme and battle dress). This is also why they are on the larger square bases.