Creditors do not have to vote but are still part of the IVA. If the creditor was never notified of the IVA they may be bound by it's terms and receive a dividend but this is not always the case.
If the debt arose after the IVA was approved the creditor is not bound at all and can pursue the debt during and after the IVA has completed.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk