The current on that ground will be on every ground wire in your house.

Not exactly true. It will just be on the grounding conductor going
back to the main bonding jumper, that one circuit. (unless you have
bonded that EGC to other circuits down stream of the MBJ)
In normal installation these are star wired.
It still can present a hazard and it is still a 250.6 violation.
Whether it would impose the 5ma considered a threat to life would
depend on the timer. There used to be a standard in U/L about how much
ground current was acceptable from a device like this but it was in
the range of 500 micro amps. I believe that has gone away tho.

We have no idea what condition the wiring is in at this DIYer's home. Given the crazy idea he has expressed about consciously creating an electrical hazard and code violation, his priority for safety sounds low. With such an attitude, it is possible that his grounding electrode system is a mess.

You are right about the standard going away for using the ground as a neutral. They found that multiple devices wired this way in a home has a cumulative effect on the ground current.

I have a chart on my web site outlining the effects of electrical current on the human body: http://www.mrelectrician.tv/safety.html#currenteffects