Question: I've inherited administration of a server (and I am not really an admin) and unfortunately there are a ton of things I've never been exposed to.

All of the parameters in the sshd\_config are commented out. ssh is working fine however. Does this mean that a default configuration is being used? What is the reason that the previous admin may have done this?

Answer: 
Yes, it means default configuration is being used. There is no particular reason, which can be connected to blank sshd\_config. May be previous admin was debugging some sshd issues.
The `sshd_config` contains all configuration options with default values by default. So the answer is that the previous admin was not doing anything with this configuration.

For the record, see the official upstream [`sshd_config`](https://github.com/openssh/openssh-portable/blob/master/sshd_config), which now contains few non-commented lines, but the older versions or openbsd versions might not contain them.