The unsafe thing is that there is no arc suppression in a wire fuse so it may not clear a fault. Also, the wire could be too large.
This is not an uncommon situation where spare fuses are scarce. The solution is to make sure that there are plenty of fuses around and that the linemen know what size to use at each location.
You might also order some leather protectors for those rubber gloves. Is he doing this energized???
its bad enough that you have people trying to kill you. If the people you are working for are trying to kill you too, its time to bail out (assuming you are just a contractor). If you're signed up, its time to send an anonymous note to IG (if they even care)