it's not officially sanctioned by GF, but allowed to continue.
let me explain.
it is illegal to sell ingame items for outside currency. ingame item == gold, outside currency == irl cash(diamonds). that being said though, having two people give each other a "gift" is perfectly fine.
in short, two people "gifting" each other itemshop items for ingame items is fine. that being said though, it is an "at your own risk" venture (exchanging gifts, remember? not a transaction. a gift does not have to be returned/reciprocated).
cheers,
cike