The 3rd party module referred to will not work with the current version of UnrealIRCd.

The current version of Unreal does have the ability to monitor pm's using the spamfilter option referenced earlier.
The spamfilter will not relay the full text of a pm, but can relay the word(s) that triggered the filter.
My experience as an IRCop and my dealings with others that are IRCops on one or more networks shows that we have bigger problems to handle than to worry about trying to monitor pm's.

As stated, if you are really worried about what you put into a pm being read by someone else, then you should find a different method of relaying that information.

While Instant Messengers were suggested, there is nothing (that I'm aware of) to guarantee that these are any more or any less secure than IRC's pm's.

If you want to ensure that only one person gets the information you are giving out, the only way that I know of, is to give it to them in person.