I posted this in another similar thread.
I think you will find out it is your phone, not SYNC that can't recognize the name you are asking for. I have trouble calling 1 person in my phone book (Sami) , it will always dial the same wrong person (Sandy). Then I got a call from Sami the name is pronounced 'Somi' by the phone, through SYNC. I called her back using 'Somi" and it dialed the correct number. My phone says 'Somi" when it is not connected to the car. It is the phones voice that comes over SYNC when a call comes in. not the SYNC voice. If there are similar names in your phone it is the phone, not SYNC that has the trouble.
I have an Instinct and can voice dial with it. I need to tell it to dial pronouncing names just as it tells me who the call is coming from. You say the names are unrelated, so you may have different problem, but can you voice dial with the phone and how does it work then?