Refugees at this stage of the game are very different than refugees later on, obviously.
I'm with ALIPW - many players stay tribeless until they find the right situation, as opposed to joining the first "hey, joinz my trib plz" email they get.
As a result of that, they may seem vulnerable, and often get attacked. I've been attacked, lost troops, etc. on this world already. But there is a huge difference between being attacked, even cleared, and being nobled - losing troops at this stage slows down growth, certainly, but doesn't make an easy noble target.
A good tribe shouldn't care at this stage of the world if the player has an incoming attack about to land at the time of the invite - if the player can be an asset, such things are merely temporary.