There are systems that do allow for this, but the most common case I've seen has been residential solar. I personally doubt that this would be possible for a no

There are systems that do allow for this, but the most common case I've seen has been residential solar. I personally doubt that this would be possible for a normal gas generator to work this way -- particularly as you said because the waves would never be in sync. At least with a solar system, you're already phase-matching the incoming AC, so could push power out at the correct phase.