Well in a radiation detector the radiation causes ionization in the gas. This charge is collected on a wire and transmitted as a pulse. It's technically creating a current so I guess one could argue that it's directly producing electricity. However even with a substantial radioactive source, that produced charge is so small it still has to be amplified by an alternative power source in order to be read by the electronics. In the end the net system uses a lot more electricity than it produces.
Perhaps one way is if you had a very powerful gamma transmitter in a box with a hole. The gammas shoot like a laser to a distant tank filled with gas. The gas is ionized creating a charge which is collected creating a current. Then maybe you'd have created a wireless power source using radioactive materials. But that system would be so inefficient and so dangerous I can't see there being any kind of commercial application.
All levels of radiation should be considered harmful. However, consider that you are currently being exposed to radiation right now. Bananas have radioactive potassium that you eat. Your bones contain naturally occurring radioactive carbon 14. Uranium decay in the ground produces naturally occurring radon that you inhale in minute traces. Then there's the background radiation exposure due to global contamination caused by three decades of nuclear bomb tests.
Radiation causes DNA damage. But DNA is capable of repairing itself to an extent so there is a level of tolerance to radiation that our bodies can endure before it begins to break down. With that in mind and the fact that radioisotopes do decay to stable elements, some very quickly, some very slowly, there are limited levels that are allowed to be put in the environment without fear of damage.
For example many medical imaging tests use Tc-99m injected into the patient. It has a physical half life of 6 hours and a biological half life of 1 day. It decays into Tc-99 which has a physical half life of 211,000 years and a biological half life of 1 hour. So after about 70 hours it's pretty much entirely out of your system. But you per it out so in that time your pee is radioactive. But since you only have a really small amount and the half life is so long, and that amount gets diluted through the whole sewer system then it's not really a big deal.
But in the 60's when they were dumping barrels full of it into the ocean as nuclear waste it was a very big deal.
In a sodium iodide detector, high energy gamma radiation enters the crystal. It elevates electrons in the crystal to an excited state. The electrons then de-excite releasing photons. Impurities cause the electron to drop in stages so the emitted photons are lower in energy, usually in the visual range. Those photons then impact a photocathode made of a specific material that is more susceptible to the photoelectric effect. This effect produces electrons which are collected and sent through a photomultiplier tube. This amplifies the charge and in the end collects on a wire to produce a pulse signifying that a radiation event has been detected. So this is one method in which the photoelectric effect is used to detect high energy radiation.