I've seen several situations in which negative or criticism feedback are channeled from a higher level manager through a lower level manager, towards an employee, in an attempt to shield the higher level manager from any negative perception of them by the employee. Is there a name for this management technique?
There is no formal name for what you've described (explicitly shielding oneself from a negative perception) as a "management technique".
Without more specifics about the situations you're referring to, it's hard to give anything more than a general answer. And in general, the more senior a manager is, the more weight her words will carry. One of the more difficult adjustments for new managers (especially when some of their reports were previously peers) is around the way that employees closely monitor the words and actions of the manager for clues to what the manager thinks of their performance.
That effect is amplified the higher up the chain of command things go.
So in the scenario you described, there are two benign explanations:
First, the Higher Up doesn't want the employee to feel threatened by being criticized by someone high up on the org chart (as an extreme example, for most people, even the most thoughtful and constructive negative feedback from the CEO is still perceived as an existential threat to one's status and ability).
Second, the Higher Up is working to coach the Manager on giving feedback, so is paying closer attention to the Manager's reports to spot opportunities for feedback that the Manager may not be acting on the way the Higher Up would like.
It's true that some managers avoid conflict because they want to be liked by their reports. And it's certainly possible the Higher Up in your situation is doing that, but in my experience that effect rarely extends beyond one's direct reports.
It depends on the situation and the size of the company. It is usually a delegation of authority similar to a chain of command tactic which can sometimes be viewed as not stepping on toes and other times is straight cowardice. If your manager is responsible for managing you, then technically the boss's boss is holding your boss responsible for managing you by ensuring the feedback is provided to him/her and not you. If that is done I would personally tell the person under me where the feedback came from and deliver it in a way that is for improvement and not straight criticism.
I have also had the opposite done to me and I personally consider it cowardice to not be honest in order to avoid any perceived "conflict". If someone is getting paid for a job, even if the boss's boss is really opinionated, the point is the job is to support the vision of the person held responsible for that vision. So opinionated CTO wins over individual contributor logic and would have to be adhered to anyway. The only reason I can see for not being honest with some feedback is hiding from perceived negative situations.
~CTO to manager - x person is a freaking idiot, I don't want them messing up y product
~Manager to employee - CTO believes you lack the knowledge and experience to do y so I would like to talk with you about how we can boost your knowledge and experience and then seek opportunities to demonstrate your knowledge and experience as vital to the team which in turn will modify the CTO's impression.
The above shows where the feedback came from without saying exactly what it was and also shows support of the individual by the manager instead of the manager stepping out of the line of fire from the abusive CTO.