I see that some pps said to do nothing about it and it will go away.
I worked in a daycare for 3.5 years and there was one family who had three children. They all had cradle cap, and with all of them, the mother did nothing about it. I was only there for the second and third child but both of them had bad enough that it itched and they would scratch their heads so hard that they would bleed. I don't know if there were underlying skin problems, but I don't think cradle cap should be ignored, no matter how little there is.
My DS is 3 months tomorrow, and I just noticed it starting. I just brushed it off (it did take a little effort and his head turned a little red, but then I stopped).
I think if you do it for short amounts at a time, but do it often, it should clear up and you won't have to worry about his head getting raw. And as for the soft spot, Joey head butted me once, and my chin hit his soft spot really hard (like it sort of dug into it) and he was totally fine, no crying or anything.