Yeah, the yokes are good. My pedi recommended starting them for DHA and for iron. Jakob really likes them too...you can actually feed it raw...runny is barely cooked at all anyway. I mix in a little bm and he has really been loving it!
I would cook it completely and then mash it up. I've heard that kids really aren't supposed to have anything with raw eggs in it. They could pick up a bacteria that wasn't killed by cooking, get sick, etc.
I fed ds (8 months) some rice pudding last week and then noticed it has eggs in it. The next day he broke out in a rash all over his body. He's had hard cooked egg yolk, though, before and really likes it.