Did Dallas know Ash was a Synth?
Could Dallas have known that Ash was secretly a Synth? He was the Captain, after all, and would have had access to the crew manifest and their individual profiles, and it's seemly common knowledge that WY sometimes embeds Synths in long term voyages. Would WY have at least informed the Captain of a ship that a Synth was on board? He does seem to defer to Ash quite a bit (yes, I realize he was the science officer, but still).
Additionally, is it possible he suspected Ash was a Snyth and that WY was interesting in keeping the xenomorph? He does side with Ash on deciding to keep the dead Facehugger (Ripley, very wisely, wanted to destroy it). Also, he had access to Muthur. Surely he was aware of the special order to prioritize the xeno and that the crew was expendable?