Vouchers are only acceptable to the value of 250 euro and after that then it is subject to BIK tax as far as Im aware.
Why should u be worried about his tax though - Can you not just give him the 400 euro and if he declares it then all is fine otherwise its on his head!
You make money you pay tax we could debate this till the cows come home.
God I hate that Irish mentality
Pay him what ever way you want.
But in relation to giving him 250 euro in vouchers that only works with employees