I usually purchase about 50-100 super worms at a time. The pet store gave me a container with a brownish sand in it. I re use it, the sand has gotten super low so I added vitasand that came with my starter kit (finally a use for it). Is this ok for short term housing? Usually feed them all in around 5-6 days.
The vitasand isn't a good substrate for keeping superworms on, no. If they do ingest it then it wouldn't be healthy for them, or for your dragon to ingest one with vitasand in it. They would hold very little nutrition.
You can make a substrate bedding out of oatmeal, wheat germ & bran flakes. Or, you can get organic chicken laying crumbles, which is highly nutritous. Then put potatoes, carrots or apples in for moisture.
When it cools down again, I will use cheap rolled oats which lasts 2-3 weeks as a substrate. However, in the sunmer I have found it gets mold too rapidly.
I'm currently using corn cob granules and has been good for the last month of so. They do not appear to be eating each other due to having an inedible substrate. They get a lot of veg and scattered oats to compensate.