The simple answer is no, until now, we haven't found any negative effects on health, and we've looked quite deep.
In order to cause any damage from electromagnetic radiation, one of three things has to happen. Either the radiation is high-frequency enough that it can ionize atoms, which leads to ionization damage, or you have to get electrocuted, or cooked.
Let us discuss the last two conditions.
Human bodies are susceptible to electrocution only at AC frequencies that are low. When the frequency becomes high enough, no uncontrolled depolarization happens, so you don't get electrocuted.
At high AC frequencies, the only way of suffering any damage would be through ohmic heating of tissue, i.e. current heating you up.
Both of these effects, though require a high enough potential difference between any two points of your body to happen, nowhere near what is radiated away by such induction heaters, or even leakage fields from big fat transformers (though I wouldn't recommend touching the output of one). The electric fields are simply not that large in magnitude.