Actually it's not a service road. It's the regular road that does the loop of all the hotels. It connects to Buena Vista Blvd at one point, goes pass the Swan, Dolphin, Yacht Club, Beach Club, Beach Club Villas, and finally Boardwalk Inn/Villas entrances, then connects back onto Buena Vista Blvd.
If you're staying at Beach Club your quickest way to anything is to exit the parking lot, turn right on the road and follow the road to Buena Vista. This takes you under the waterway that connects the Epcot area resorts lake to the Epcot lake itself.
For some reason many people think they have to turn Left out of the parking lot and go the long way around.
Just off the hotel access road there is a warehouse area behind Epcot's Canadian/Great Britain areas that does have some truck traffic.
Finally to answer your question, we never heard any traffic that was bothersome, and we had a great view of the Epcot fireworks!