A Question of Ethics

I hear lots of people talk about ethics and all kinds of statements regarding who is being unethical. I'd like to consider a not-so hypothetical scenario

There is a consulting company - they have specialists that do work in a certain area that clients pay for, the industry isn't important. One day one of the consultants leaves and heads off to a frontiers unknown.

Let's say a few weeks later one of the company's current consultants searches for and finds that ex-employee's name active in one of your client's user database. This current employee who is currently working with that client, recognizing the name of your ex-employee (he did search for it) contacts the customer and says - hey why is this person's account active? The customer says - "well after we learned he left your company we reached out to that ex-employee and offered him some consulting work".

Now the employee that left had previously worked with this client in the past as part of the consulting company. The employee did not leave to work with this client, and did not get work from the client that you necessarily wanted. This was not full-time consulting work or the ex-employees primary employer.

But the company president doesn't know those details. All the president is told is that his ex-employee is now working with one of the company's clients where a damaged relationship exists.
Thus the president of the company decides to contact this ex-employee and tell the ex-employee how upsetting it is that the ex-employee is willing to compete with the company (the parting was on good terms) and take work with one of the company's clients. The president gives the ex-employee an earful and maybe the president even considers a call to the client to give the client an earful. But the ex-employee says - "hey not true I didn't leave to take your work with this client" and even goes so far as offering to let the company have the work (since it's only part time) and even offers to try and work with the client to improve the company's already damaged relationship with the client.

The question; Where are the ethics violations?
Is it ethical for the ex-employee to have done work with your client? (making clear all parties agree there is no illegal relationship)
Is it ethical for your current employee to dig the customer's user database to find an ex-employee and then report to you about the presence of an account?
Is it ethical of you to contact the ex-employee and claim they should give up the work the client contacted them about and offered to them?

I have my opinions with regard to the fact that I think the one who is ethically in question is the employee who took a customer's proprietary data and used it to find an ex-employee in that data, but I'm open to other opinions and debate - but you have to provide any specific context you want to use to justify your position, since my context is a real world scenario. (and no I'm not involved I haven't changed jobs in excess of 5 years and don't have any current plans to do so, I just know one of the parties involved as a friend and don't want to identify parties even by implication)