There is no need for Hook to hear/see previous Dark Ones, as his Dark One-ness has come from the corruption of Merlin’s magic. Emma said she would use Merlin’s magic and the flame (not sure how those two things go together, but I’m willing to go with it) there are no Dark Ones in Merlin’s head and therefore no Dark One’s in Hook’s head b/c the magic that brought him back to life (thether his life to the blade) was once light. Merlin’s magic came before Nimue’s magic so there are no previous Dark Ones to see. Hook’s a new type of Dark One, like Nimue’s Dark One-ness which was a corruption of the Holy Grail’s magic.
Hook has been pretty angry this season in Storybrooke, lots of yelling and arguing and was quite happy to make Arthur pay for lying to them (this was before he knew of his Dark One status) If he’s not sleeping, he can write it off as being worried about Emma (which is perfectly reasonable. I’m sure they’ve only had a couple days back in SB after being in Camelot) And without Dark Ones in his head pushing him into using his Darkness, again he can write it off as his own personal demons giving him dark thoughts. But once he’s been shown it’s not his own thoughts, he can indulge. And why try and use magic if you don’t know you have it? Emma needed to be really pushed for her magic to surface the first time.
If one is to engage with the primordial forces of darkness, one must expect a little social awkwardness