No, the keys mappings during the record just terminate the recording and advanced to the after recording menu options. The keys that are mapped during the greeting on the call handler/subscriber do not carry foward into the recording conversation.
By default after the custom record greeting is played for a subscriber there's a system prompt that plays indicating to record your message at the tone and either hang up or stay on the line for more options. If that's playing after the greeting (which it is by default unless you manually whacked it) that's a pretty long runway for someone to hit "0" there... you _could_ add some silence onto the end of that or lengthen it or something but I'd kind of raise an eyebrow if someone told me they needed more time to react there...
