Short answer: Yes.
Long answer:
Fantasmic is nearly a half hour long. However, that doesn't mean you will be out of the theater by 8:30. It can be pretty congested getting out of there. Unlike entering, where people arrive spread out over at least an hour, most people try to leave as soon as the show is over. However, you should be out of Fantasmic by 8:50 at the latest. Exit the park and walk to Epcot along the river. I think that is a little over a mile walk. If you are in good shape, that is no more than a half hour walk.
If you have to drive to Epcot, then you have more delays involved with trams, parking lots, and roads. Driving will also require you to enter Epcot far from the fireworks area, while the walking Epcot entrance puts you very near the fireworks.
You can also take a boat from HS to Epcot. There is some randomness involved with this, though. How long until a boar arrives? How many people are waiting to board before you?
If you are up for it, I suggest walking. That's what I would do.