Steam guard on for at least 15 days to trade - Requisite to gift?

send it to the email yes. His loss if he gets hacked.

I'm positive you can send it via e-mail since that's what I did.

email

Why would you take SteamGuard off to use a site?
SteamGuard is there to add an extra layer of protection by giving you 'device control', in other words to log in on a new device you need a security PIN.
Accessing a page like SteamGifts, Backpack.tf, TF2Outpost.com, etc. uses Valves own API to log in using as little of your account information as possible (a username and authentication number) to keep your account safe. Turning on/off SteamGuard makes no difference once your browser has been added to the SteamGuard list.
Unless he's accessing SteamGifts (or any Steam-related webpage) on a public computer, he shouldn't be turning on/off SteamGuard.

As for your question, you are still required to gift the winner. They are not required to add you to their friends list, and I believe the rules even state that you are to email the gift to the winner.

Why take SteamGuard off at all?
Is it interfering with normal operation of Steam or games?

I must be doing something wrong since I haven't had any errors yet. :P