The discharge produces crazy amounts of UV, but they carefully put a glass tube around it to cut as much UV as possible, for safety reasons. A bare HID lamp with no UV barrier will give you sunburn, conjunctivitis and all sorts of other issues in just a few minutes. The big "mogul base" glass tubes are (I think) fairly effective UV absorbers, plus the large outer tube acts as an insulating layer so you don't want to just smash it off because the inner envelope probably won't be able to get up to temperature any more.
You might be better off looking for a bare bulb that is designed to be installed in a larger enclosure where the enclosure is responsible for UV blocking. The drawback there though is that the larger enclosure is also responsible for containing explosions, which is how about 5% (more for the cheap chinese ones) of HID bulbs end their life. You really don't want to have one go off in your darkroom without some protection around it; there will be shards of molten quartz and metal raining down with more than enough energy to set anything papery (or human) alight that it lands on.
You may be able to get a bulb with an all-quartz safety shield, which would have significant UV output.