Being in the water treatment business, I am reasonably familiar with the EPA's "lead and copper rule", and the whole Flint, Michigan debacle.
Lead can leach from lead pipes and lead solder, and copper can leach from copper pipe or tube if the pH and corrosivity of the water are bad.
But in our case, for these smoke generators, we are not even dealing with corrosion or leaching. So it is simpler to understand.
All we need to do is keep copper or lead from vaporizing. If they don't vaporize, they cannot leave the surfaces and contaminate the air/smoke mixture.
So keeping the temperatures below those where the vapor pressures of the materials in question become high enough that they vaporize to a dangerous degree is all we have to do to be safe.
Fortunately, the temperatures at which lead and copper vaporize to a dangerous degree are rather high.
Can you put your hand on the copper pipes of these generators when they are running? I would guess so.
And the inner venturi tubes are constantly cooled by the air from the compressor or air pump. So we know they stay cool, as well.
I serously doubt that much copper or lead are vaporizing into the smoke/air stream in these designs.
Stll, why not use lead-free plumbing solder just to make handling the unit a bit safer. Most people are not very sensitive to copper. The MCL (maximum contaminant level) for copper in drinking water was set, in part, to accommodate people with Wilson's Disease.
The only thing that comes to mind as a route by which we could poison ourselves with these gadgets (with lead or copper) is if water vapor condenses on the lead or copper, corrodes it, then drips down onto the wood chips or pellets, carrying the dissolved lead or copper, and is then raised to a high temperature as the wood burns. That might vaporize some of that lead or copper.
That seems pretty far fetched. But I guess anything is possible.