Yes, I use that check box, all the time.
A word of caution, however....
After creating a listing, and posting it to ebay, I then click auctiva's link that reads "create another similar ad".
In doing so, a new form opens up, with everything just like the previous ad, including the "Optional ebay gallery images" box is checked...however, the photo's that are about to be posted to ebay's gallery are the same photo's as my previous ad, even tho I select new auctiva images with this new ad. You always need to uncheck, and then re-check that box, in order for auctiva to submit your new ad's, new photo's.
Hope that makes sense. Just be sure and look closely at what photo's auctiva is about to hand to ebay's gallery. Make sure they are the same images that you are using in the current ad you are creating, and not from the previous ad.