B.L.E., the vapor pressure of lead at the temperatures we work with is so vanishingly low that there is virtually no vapor present beyond maybe a centimeter from the melt.
For lead, the vapor pressure at 700 degrees F is about .0000001mm Hg.
You can't compare the behavior of liquid water and liquid lead because their vapor pressures are completely different at their melting points. At the melting point of water, 32 degrees F, water has a vapor pressure of 4.5mm Hg. At lead's melting point, it's vapor pressure is 10e-8mm Hg.
For comparison, water and lead at a boil have vapor pressures of 760mm Hg (one atmosphere).
A commercial lead pot isn't able to head the lead up to a temperature that would cause harmful levels of lead vapor. You'd have to approach a couple of thousand degrees, I think.
On the other hand, if you're melting wheel weights, all the nasty crap that those things are crusted in ought to be worrisome - lord knows what kinds of carcinogens and toxic gasses are in that smoke.
Well we don't rent pigs and I figure it's better to say it right out front because a man that does like to rent pigs is... he's hard to stop - Gus McCrae