Here I am on my fourth character, just completed goodsprings, of course I'm thinking I've got some experience under my belt from the first 3 play throughs, or so I thought.

Just to set the scene I've used geck to build a dwelling several meters down from goodsprings source, now I spent 3 in game days at goodsprings preparing to venture past the last chance to change your appearance and stuff, all is going well, I know the geckos have returned by this time, but I'm not worried, I make a beeline for the dwelling and head inside closing the door behind me, safe!, uh no, the geckos came after me opening the damn door, 3 hunters and they gave me a right good pasting before I managed to kill them all, anyway I survived, but whats with geckos being able to open doors?, they will have lockpick skills next.

Veloci-geckos?

Yes, they should rename the hunters, at least it now explains why I see them scratch their heads in thought.

it is not that hard to push open a door, my cats can do it, but one of them opened a locked door somehow, so yes animals lockpicking very possible

I saw http://www.gamesas.com/index.php?/topic/1140580-victor-got-visitor/ and other time, I was chased by deathclaw in to another shack. Was quit a mess to be in small shack together with angry deathclaw

If you look in to the GECK you will find that creatures and NPCs have flag which sets if they can open door. Most of the creatures can.