Lowering springs = can’t use bump stop?

I would suggest definitely tighten all bushing mounting hardware with suspension loaded, no matter the material they are made from. Just too important of a proceedure not to, at least to me. I have never encountered an instance when it wasn't possible to do so. Maybe not always easy to access hardware, but do-able. You can always let suspension down and double check your torque, if you felt your leverage/tool choice was inadequate enough with it loaded.