I always use the combo DSLR + slave flashes but in my case is the equipment I have to digitise everything in every museum I work in (since small CDV photos to big maps/tables and furniture).
As said, light damage is accumulative. And the flash lux level, even if high, as a too small duration to compete with the long exposures of natural/artificial light of workspaces.
So I think the answer must be: the way you find the less time consuming and the safer to photographs. If you have to digitise a lot of them, you must stablish a workflow that allows you and your partners to do it with the less time loss possible. To buy/use a high quality scanner can be money consuming and to use a DSLR can be space consuming… so its a personal choice.