No pulse would be detectable that is correct. An AED may or may not shock depending on how coarse the v fib is - very fine v fib can be mistake. for ash time and no shock would be administered. CPR is always indicated between shocks and for a full 2 minutes after every shock before a pulse check
An AED will not shock a stopped heart. If they are doing compressions, there is NO rhythm. If there is a bad rhythm the AED will shock into normal rhythm. Otherwise it will tell you to do compressions until some kind of rhythm is detected.