I think they are stretching a point , I am in a seismically active area and have never heard of this. The inspector "feels" they could skip across the floor? You are correct about it being difficult to fight City Hall, it is also difficult to reason with idiots so you have a double whammy.
However, his 'skipping' across the floor is baloney and depending on how friendly the people who know about siesmic stuff are at your local university, if you have one, you could get data to validate or invalidate the skipping scenario. In a seismic event (I always thought they were called earthquakes) it is the ground that moves either horizontally or vertically, it can move fast and in the 1972 earthquake in Southern California (I think it was '72, it was the one that knocked down a Veteran's Hospital I think) accelerations of greater than 2 g's were recorded and similar values occurred during the Northridge quake. With these accelerations the ground slides sideways under things so it is the ground that is skipping around not the machine. But the ground does not move very far and this is where a university seismologist may be able to give some information. There will probably be records they can refer to to find the maximum lateral displacement that has taken place in prior quakes in your area. If the machine is further away from any walls than the maximum displacement ever observed no-one is going to get crushed between the machine and the wall. The wall might fall down and crush the person but that is a different matter.
However, having bored you with a bunch of stuff I will say what I would probably do because it is always a losing thing dealing with idiots. Did your machines arrive on shipping pallets? There are bent metal straps that are held on the levelling screws and bolted to the pallet. I would simply level the machine then install these metal straps in much the same manner they where on the pallet but they will be bolted to concrete anchors in the floor. You can tell the inspector that they machine is secured even more firmly than it was for shipping because now these straps are secured in concrete not wood.
An open mind is a virtue...so long as all the common sense has not leaked out.