Well I do like to lean towards being safe,, but who drinks the water from the hot water tap?? The only way a person could get poisoned is if the domestic hot water coil leaked, or in my case the plate heat exchanger. The water in the boiler is at a maximum of 15 psi, [usually about 5psi], if it developes a leak, the house water pressure is going to over pressurize the boiler,, and blow off the pressure valve..
And if for some wierd occurance, and the house water pressure somehow got to be lower than the boiler pressure,, then the only water contaminated with glycol would be the hot water,, and I don't drink water from the hot water tap,, or drink water from the shower head...
IF I was going to add newly purchased antifreeze,, I'd go with the non-toxic stuff,, but I'm certainly not concerned about my system with automotive glycol.