Tax man has no interest in an iva unless you owe them money.
However it is best to tell your accountant if you are in an iva as it helps them understand how to help you.
IVA started March 2011, Completed March 2016 and certificate issued 11 days after final payment. It was not always easy but then some of the best decisions aren't.
No, unless, as lifenoteasy says, they are a creditor in which case it might come up in the normal course of business / correspondence with the accountant as your agent.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
No but As Foggy says if the accountants were owed money and listed as a creditor they will receive updates from your IP. I would have thought your accountants were one of the people you could talk to openly about the IVA.