Yes, but that wouldn't save any time. The Poly boats don't operate any earlier than the ferry. The ferry can also accommodate many, many times the number of people than the Poly boats can. If the monorail is not running from the TTC, then it won't be operating from the Poly.
The ferry may not be as fun as the monorail, but I've found it to be just as quick or quicker than the monorail between the TTC and MK, counting the wait time, loading/unloading, etc.