I dont think it is negative when surfers come to your hub and see all of your own galleries , your sale potential might be inreased .. Maybe he'll find your other galleries more appealing than the one he came from and signs up.
Galleries are harder that Freesites because most are linked through the TradeScript Code which make the not ( all ) appear in search enginges, while fressites are all linked directly.
I think the idea with the hub is good , for every sponsor / site a new hub page
