There is no unified way to differ a booking or a block within ical type of synchronization. All unavailable dates are imported as bookings/events. With HomeAway you may be able to recognize bookings if the Booking Log contains a guest name.
The export iCal seems to differentiate between booked and blocked dates and includes booking dates in the ics file but does not include dates blocked from within the Hotel Booking plugin. Is there a way to ensure all unavailable dates are included in the Hotel Booking generated ics file?