Yes, but . . .
This is from the 2004 edition of "Birnbaum's Walt Disney World."--p. 211.
"Bikes are available for rent at Fort Wilderness, Old Key West, Wilderness Lodge, Port Orleans, Caribbean Beach, Boardwalk, and Coronado Springs.The cost is about $8.00 per hour or $22.00 per day; tandem bicycles are offered at SOME locations."
Thus, they are available at some of the locations, but not all of the locations, and the book doesn't say which ones.
I hope this helps.