I dont know how much interest they would have in kuokkanen considering he would be a fringe player for them. Maybe if he was still on ELC and wasnt waiver eligible, but not really any point if he is making 1.9 mil.

Would love to have Vanecek with the Devils, but rather move Zacha than Kuokkanen for him.

Why ?
Zacha > Kukannen
And Zach has moremtrade value too

First off, if Caps would take your suggested trade for Vanecek I would happily go along with it.
I just think Zacha would be a better fit and provide more value for the Caps than a 3rd + Kuokkanen and not sure they'd take that for either Sammy or Vanecek.

Anyway, Zacha is likely done in Jersey.
Years of failing to live up to expectations and overall inconsistency makes it more difficult for the Devils to sign Zacha to a new contract.
Basically, it is mainly due to that fear of the NJD front office not qualifying Zacha and not getting any value for him that makes me want to move him before Kuokkanen.
And there seems to be a place for Zacha with the Caps, whom in return are looking to deal one of their goalies.

Kuokkanen is the inferior player between the two today, yes.
But he still has room to grow and develop.
Only two years in the NHL so far, good rookie season, weak sophomore (also, bad luck with injuries).
While he currently is the 13-14th forward on the depth chart, I think he can carve out a big role with the Devils next season in a bottom six capacity.