This article provides several examples where popular apps have been rejected just for having a mic icon in the UI. When the icon was replaced with another icon, the app was approved.
http://www.addictivetips.com/ios/does-interface-matter-in-app-submission-approval-by-apple-case-study/
All the app shown in the example have used the iOS Siri/dictation icon to do something other than launch Siri.
Also, why is everyone using that mic design? Very few real world mics actually look like that anymore. Why not use something people are more familiar with like a standard dynamic mic shape?