(I’m going to put in a separate feature request with Crayon Syntax Highlighter, which we are using to highlight code on bbPress, asking if it’d be possible to ignore HTML tags inside code tags (both square brackets and the more future proof pre tags), but that wouldn’t be the cleanest solution.)
The better solution would be if the importer could prevent this from happening in the first place. If not for square code brackets (although this is a standard set by an Automattic plugin) then at least for pre tags.
In my tests, I embedded code in pre tags in a BuddyPress forum, imported it to bbPress and the embedded code was now populated with HTML tags, mainly br tags for the newlines. Funny thing is if I have the rich editor turned on, I can go into edit mode with a post that has code embedded, then I’ll go to the “Visual” mode and back to “HTML” mode, and everything has been cleaned up. I basically want the importer to do that step for me.