How to tell which Indexes are not being used?

You could also consider capturing the current indices, and then dropping them, restoring them once your load is complete.

I do this on some loads by generating a create index script using dSQL and storing it in a table, for each index on every table. Once My load is complete, I do the reserve, pull those scripts out and re-add them.

Since the script to generate the create scripts would run prior to each load, it will be self updating, and reflective of any new indicies they've added during that day.

hth