I'm more on the software side for HV system studies, but I have seen consultants and utilities do put ground loops on MV ground mount transformers. Some countries also study/measure the touch voltage that could occur for those MV sites.
All of our transformers sit on concrete vault that has the rebar internally bonded. The vault is treated as an ufer ground, and it has internal bonding/grounding lugs to attach to the cable shields.
The vault lid is only somewhat larger than the transformer footprint, so it is unlikely someone would have room to comfortably stand on the lid. The details of vault grounding are available at