When able to play highway or recruiter using captain (after highway discount) no discount benefit or villager gain (respectively) is conferred. Perhaps due to those cards not usually being playable with captain before discount?
Highway reads:
Quote+1 Card
+1 Action
---------
While this is in play, cards cost $1 less.
Note the "While this is in play" clause below the line. When you play Highway with Captain, Highway is not in play (Captain keeps it in the Supply), so it's cost reducing function is not active.
For Recruiter, I just checked this and it worked in the scenario I tried. What I assume happened is that you trashed an Estate, but forgot that the cost reduction from Highway had reduced it's cost to 0, so you don't get any Villagers then.