I read that uranium was used to colour glass as far back as 79 AD, meaning that early civilizations had access to it, so is it possible that it or other radioactive materials were used for weapons in the pre-atomic era?
Physics is my area of specialty rather than history, but I can comment on the danger of radioactive materials. Radioactivity was only discovered relatively recently, in 1896 by Henri Becquerel and Marie Curie, and before this there was little conception of radioactive materials being dangerous - and even after. Shoe shops would use x-ray machines to check the fit of your shoes, which anyone today could tell you is insane. This should tell you that, even if a pre-modern society had any conception of radioactive materials being dangerous, it would not be because of any conception of radioactivity being dangerous - it would be as a simple poison. It is impossible to refine radioactive materials to such a quantity that it's dangerous to just be around them without centrifuges, or gas-diffusion refinement. Without that a lump of uranium ore is more useful as a rock to throw at someone than as a radioactive source.
The only way for a radioisotope to be significantly dangerous (over a short period of time, you can still get increased cancer risk and other long term health defects from low intensity gamma rays) without refinement is if it is ingested or breathed in, or it occurs in such large quantities that it contaminates the whole landscape. There's an excellent comment on a previous thread regarding uranium in Australia here from /u/toldinstone ( https://www.reddit.com/r/AskHistorians/comments/t5tqc0/did_the_ancient_world_have_any_chernobyls_that_is/hzaa9q9/ ) which shows how there can be a pre-industrial understanding of the danger of radioactivity, but it's in the context of a whole region being considered evil, or cursed, or risking the anger of supernatural entities. Radioisotopes generally don't occur in nature in that quantities though, as by their very nature they usually decay out of existence in a few years. Uranium is relatively unique in that it contains such long lived isotopes in such large quantities though.
No. Both because radioactivity was unknown, but also because the level of radioactivity a human could be exposed to pre-atomic era was low-enough that you'd barely notice, much less be able to weaponize. By "barely notice," I mean that over centuries there were some who noticed that uranium miners in what is now Czechoslovakia seemed to contract lung disease (later identified as lung cancer) at higher rates than normal. To be a useful weapon you'd need something that worked a little more directly and acutely than that (in any event, there is no way to weaponize radon gas, which is what was causing those cancers anyhow — even if you wanted to, it's not a possibility).
Uranium ores, in other words, can be radioactive-enough to be a chronic health hazard, but not a weapon. To make things that are radioactive-enough to be a weapon, you generally need a nuclear reactor.
More details on the lack of knowledge of radioactivity are here, but the main takeaway is that people weren't in contact with highly-radioactive sources prior to nuclear technology.