What are the guidelines for drilling holes through rim or band joists?
I have never seen an issue with cutting through a band joist. HVAC guys will gut a whole section with reckless abandon, so it seems. If you are not cutting into the joists, you will be fine. I never had an inspector cite a band joist not being cut properly.

It might be wise to make the hole so there are at least 2 joists at least on one side of the cut. The band joists are to stabilize the end of the joists.

I would make the hole larger than 8" for an 8" duct. 8 1/4" minimum. All this assumes the band joist is fully supported by a foundation wall and is not spanning over an area as in going from pier to pier...