If there is a potential code issue. maybe deal with it later. Are you reading between the lines?I would find out the exact code so you can get as much space behind the pad as possible. If the term "retaining wall" becomes a issue with the code then you could most likely at least terrace it to give some extra space back there.
They will certainly be able to install a wall or terrace after the equipment is in However it would be to your benefit to have the wall done first. It will certainly cost more to have to work around the equipment and there is always the possibility of a careless worker damaging something on the pad.