There's a privacy setting to let people block others searching their journal, and the local search is separated out from public search indexing, so somebody can block search indexing but still allow searches using DW's engine. I think if somebody blocks searches, they shouldn't show up in this, but otherwise, it should be okay.

I just tested searching someone in my circle's journal with a word that I knew was in locked posts, and those posts came up. So, I think we already CAN search locked posts on other people's journals if we have access to those posts, just as people can also already block that.