Correct for the most part. You can still have very high relative humidity with a low WBT if the dry-bulb temperature is equally low.

When the WBT gets above 35°C, it's not only dangerous, but positively lethal when sustained for even the healthiest person as sweating (or any other form of evaporative cooling for that matter) can no longer keep the body at a suitable temperature.

WBT is also not to be confused with wet-bulb globe temperature (WBGT), which is an index for heat stress that also takes into account the effect of sunshine among other things. It's much more situational and best suited to judge the heat stress of athletic outdoor activity in sunshine.