Dining in the Haven restaurant for non-Haven guests is at the discretion of the concierge. If the Haven is at or near capacity, the concierge might deny the request. Try to co-ordinate with the concierge as early as possible. The concierge might allow the first few requests then deny the rest.
As for the rest of the Haven (lounge, bar, pool, sundeck, etc.), the non-Haven guests are not allowed there.