Yeah, if you miss atleast half (and if you only own the basegame you will miss way more then half) i think you should be okay to just enter and offcourse i can't trace back all those giveaways but i seen several mods having said the same thing that it was okay.

It's the same self made rules like delete this giveaway if the key doesn't work. Be honest, it's not like the gifter is gifting this game with all his money as a steam gift, it's probably some key, and most selfmade rules just doesn't hold ground.
IF he really would make such a fuzz about it, then he could have made a giveaway through the forum with this set of rules.