Ø Using the redaction add-on is there a way to show/hide redacted content based on a function call (e.g. so users with certain permissions in our application could see this content, specifically in the web viewer)?
No, this is not possible since it would defeat the purpose of redaction (i.e. to permanently remove redacted content). With permissions there is always option to go around the security to uncover sensitive content.
I guess you could save two versions of the document (a non-redacted and a redacted) version. Users with sufficient permissions could access the redacted version.
Ø Can content be redacted through code using a simple text search, say we know an SSN in our documents, can we search our documents for that SSN and redact them without needing the user to do it manually, short of image based documents that aren’t indexed?
Yes, this is possible. You would use pdftron.PDF.TextSerach class for search (e.g. using regular expressions) then you would use bounding boxes of matched results to programmatically apply redactions.