Since the om broke the nc request I plan on contacting him to let him know I plan on speaking to his W about the A .Do not give him advance notice. Just do it. The only reason I can think of to let him know would be to see if he and your WW are still communicating. Since you already know he's initiated contact previously you stand to gain nothing except giving him the opportunity to craft his lies to his BW.
Regarding the email from OM to your WW it is clear you understand she is not transparent. She should have volunteered that information instead of requiring a game of 20 questions before admitting. Unfortunately you know from experience there is likely much more to the story. She realized you knew something was up so she admitted to the email. She admitted to what she had to in order to placate you. I suspect there has been renewed contact between them. In addition to letting OM's BW know about the email I would suggest you go into stealth mode and see what else you can find.
p.s. Be prepared. Since you questioned her your WW may have already given OM a heads up that you know about his email to her.