I am considering establishing a blog on an independent server for
employees to discuss work-related and employer-related issues outside
of work time and using non-work computers. Discussion would probably
be highly critical and may include employers' names and details of
conversations and work-related communications. In some cases,
discussions may allege illegal or unethical activities by employers.

The employer in this case is in Oregon and is a county government agency. 

Aside from the published administrative work rules (which I can study
myself), what are the legal ramifications for employees and for the
blog host? If there are no work rules specifically restricting
employees' rights of free speech, can an employer discipline or
dismiss an employee for what s/he says about the employer outside the
workplace and on his/her own time? Are employers covered by libel
laws? In the absence of a signed confidentiality agreement, are
employees subject to an implied confidentiality agreement?

I understand that the scope of this question is probably large.
References to publicly available resources would be an acceptable
answer.

Not a lawyer .. Just a comment...

If your discussion is verbal and outside the company. Deny Deny Deny.

If it is written and there is proof there is the instance of
lible<sp>. You are covered in some instances under the 1st admendment
BUT when writing about someone else it is best to add the line.

IN MY OPINION.... you need to add disclaimers that let people know
that what you are speaking of is true to the best of your knowledge
BUT you have to put this statement to cover yourself.

I got screwed on a car deal and I put up a web site and to make a long
story short I was taken to court and because of my disclaimer I was
safe and he no longer owns the dealership... But that is another
story.

There could be so many answers to your question based on what
agreements you signed and how classified? the material is?

BUT I say when I am outside of work my time is my time.

Thanks
Steve

For the sake of limiting the scope of this question: assume that no
confidentiality agreement was signed and the administrative work rules
do not deal with confidentiality other than the obvious requirements
related to HIPAA, personnel records, customer confidentiality, etc.

I was employed by a UK division of a US Corporation. In answer to your
question, visit: http://www.pressagent.co.uk