Err...kind of...there is one route that goes from MK to the GF to the Poly and back to MK (no Contemporary). There are other routes that go to WL and FW. There is also the ferry to the TTC. Yes, you can get on the boat to the GF, get off and walk to the bus stop. The GF dock is on the far side of the resort, so I don't know if you would really save you much time compared to any of the other routes.
In the end, it's probably six of one, half of dozen of another in terms of time and distance. Given that you want to go to DTD around the time the park is closing, expect long lines at any of the MK transportation venues (boats, monorails, buses).
You could:
-Boat to GF, but you'd have to wait for the boat and then walk pretty much the entire length of the resort to get to the buses. The launch isn't large, so you might end up waiting if there is a line. Also the boats cannot accommodate
ECVs (it's a small launch).
-Walk to CR; it's about a half of mile from MK bag check to the CR valet station (the bus stop is a little closer). Then you'll have to wait for the bus to arrive.
-Monorail to CR; you'd have to get off the monorail, take the escalators down to the ground floor and then walk to the bus stop.
-Bus to any other resort, bus (or, if available, boat) to DTD.
Personally, given that you want to head to DTD around the time MK is closing, I would either walk to the CR and wait for the bus or walk to the CR and spring for a taxi.