Freezr has the ability to receive MIDI notes and operate. You can use this in the standalone version of your iOS app.
However, when using it as an AUv3 plugin, I don’t know how to send MIDI notes.
I’m using AUM as a host, and effects that accept MIDI notes will usually appear in AUM’s MIDI routing, allowing you to send MIDI notes and CCs from any device. Since it is not displayed here, I cannot send MIDI notes.