Are people allowed to do PSN code giveaways here too?

No.

Its SteamGifts cause its Only for Steam games .

You can give it away via some raffle or smthng in forum if u want , but not in Direct giveaway using the site system

Not using the gifting function of the site. But, you are perfectly welcome to give them away via the forum, groups, chat, etc.

Well, the answer is already here. Just be aware that even trading PSN keys will be slow since they aren't the focus of most users here.

You may use the forums as a means of forming a raffle of some sorts, but the site itself does not support such activity natively. This is due to the fact that there would be no way to verify that the code in question has been redeemed, which is one of the key tenets of this site.