If you are not experiencing issues with command recognition, specifically, then as mentioned that warning can be ignored.
To be clear: the message regarding Nahimic is unrelated to the message about "ATC recipients". As also mentioned, that message specifically pertains to the speech recognition engine, which is the component used to recognize spoken commands.
Once a command is recognized, there is no further involvement from the speech recognition engine, and that command is then processed further based on the instructions in the profile, which in this case is a third-party profile.
The "There are currently no ATC recipients available." message you are seeing is not part of VoiceAttack itself. VoiceAttack is merely displaying a message it is instructed to display by a third-party addon, I.E. any logic behind that message would also be part of said third-party addon.