I don't know if this is necessarily true. I would think that if the raisins were cooked at a high temperature, they would actually burn instead of just dehydrating. I'm pulling this info right out of my rear, but my intuition is that raisins are heated at a low temperature over a longer period of time (days) instead of being heated at a high temperature over a short period of time.

Regardless, I think a good rule of thumb is that your basic cooking ingredients should as much as possible resemble nature. So in this case, raisins are much closer to something found in nature than agave is. If you're really concerned, though, you could always try making your own raisins from grapes using a dehydrator. I haven't a clue how long it would take, but I might try it sometime, just to find out.