Hi Ryan,
Yes you can definitely allow job posting from employers directly into your JobRoller installation. Also built into the theme is integration with Indeed.com, and an optional plugin for a
Simplyhired feed also available (you can read more about this
here).
The "Apply Online" link allows the job seeker to contact the employer and apply for the job, but once the communication has started, the employer will have access to their email address, and likewise once the employer replies to that initial email, the job seeker will have the email for them as well.
Again regarding communication, the only option currently available in the theme is as mentioned above, so having other methods to contact each other would require modification of the default theme on your part. Thanks.