Can't encrypt them as far as I know in saved search.
You can just remove those saved searches that send those scheduled email.
And Instead Create a script which sends that email.
And in script parameters you can set the search id, recipient, cc, etc as parameters.
And create deployments for each saved search.
Auditors will not know, most likely unless you go and exclusively tell them.
Encryption might be possible in script, never tried though.
Also if you are generally concerned about audit regulations then it's better to let the user download the report from Netsuite itself, this way you will know which all users are actually using the data, at what time they fetched the data from Netsuite. Sometimes it comes handy.