Evaluation criteria for 3-minute teaching demonstration over Skype?
The easiest thing is to ask what  the criteria of evaluation is. Given the small time they probably want to see if can you actually teach something in three minutes. This take incredible content and communicative mastery to find a topic that fits within this time limit and can be explained. The typical expert knows too much to share with such direct and concise simplicity.

In relation to visuals, I would have one as a maximum that I might explain to my audience. I would  not try to do any active learning because just explaining what to do will take up all the time and there will not be any time to discuss whatever you had them do.

You  could consider asking a question or two during the demo. However the question should not be open ended because of the time constraints. You want to use the questions to lead to the goal of the lesson.