What was the answer??? The replying post has been deleted!
I think there hasn't been an answer yet and the OP just wanted to thank potential posters in advance. Edit: I'm sorry, I didn't notice at first that this is an old thread.
My understanding is that you always spawn from the blip piles. The only time you take cards from the Genestealer Deck besides travelling is to resolve the The Swarm event card.
Someone please correct me if I'm wrong.