Good questions. I'd recommend setting up a free email account for use when you submit to these directories, because it can't hurt to take the precaution. I'd do something like
mortgagebrokerland@yahoo.com for mine, instead of using a mortgagebrokerland.com email address.
As for someone trying to hack into your site... who's to say? As long as your site is public on the web and people can find it, there is some risk. Simply listing in these directories won't significantly increase that risk, in my opinion. However, staying up-to-date on all the latest security patches, having a good firewall, and a solid IT plan will help eliminate most threats.