Your answer is largely determined by the degree of felony for which he is under supervisor for. There is a possibility of credit towards supervision for when a person was on supervision before they took a plea and then they are given more supervision as a plea however, with a "violation of probation" it is not likely that there will be a reward for the failed probationary term.

They can but they almost certainly won't. There is no credit for time served on probation (or CC). You only get CTS for time actually served in jail. I hope that I have been helpful in answering your question.

I would have to read all the relevant documents in order to answer this question. He violated and got 3 more years. That is what it looks like to me from what you have written. It may not matter because he violated.