Lake hasn't even seen the field yet so he is way behind and will have a tough time making the team. Not sure how Yeast is doing but at least he is getting reps.
Seems to me if Rams are considering trading Rapp that means that Scott is going to start and that they are confident in Burgess as the #3 safety. $2.5 Million for a #4 safety or #3 safety who rarely sees the field is much to high and would dictate a trade. However if Rapp is going to see the field regularly and is seen as a everyday contributor to the defense I think they will keep him.