From my experience, (not much) I have found that if I list an item on eBay with multiple pictures, and relist it from Auctiva because it did not sell, I will be charged for extra pictures. If I list originally from Auctiva, I get the free pics.
Auctiva puts the extra pics in the description area of your listing, that is why they are not with the other (gallery) picture. If you originally list in Auctiva and relist in ebay you won't be charged for the extra pics because ebay only recognizes one pic.
I believe this is correct, at least this is what I have found to be true on my listings.