You can get more raisins into a 1/2 cup if you pack them tightly.
So, when a recipe calls for 1/2 cup of raisins, should I loosely pour them into the cup measurer, or pack them tight?
If the writer has chosen not to mention this, it implies that either it doesn't matter (most likely, for example if the exact amount of raisins is a matter of taste), or it's badly written, in which case all bets are off.
I did an experiment using British style sultana raisins (which are slightly different from US sultanas) and a 200ml cup. I found that 1 cup of loosely packed raisins was 120g and tightly packed was 155g. So for a 118ml ½ cup, loosely packed raisins would be 71g and tightly packed raisins would be 91g.
For comparison the website linked in another answer gives 80g for a half-cup The variation of -9/+11g would hardly be noticeable in a fruit cake.
Raisins, are a natural product and will vary depending on the variety of grape used, some will be slightly sweeter, or more acid. So even if you use exactly 80g, you will get some variation in result.
So for ½ cup of raisins you are free to pack them in, if you like a slightly more raisin-y mixture, or not if you don't. You are also free to use 80g on the scales, or go crazy and see what the result of using ¾ cup in the recipe. It probably won't be a disaster.