Can a 94 Cadillac DeVille 4.9 engine fit in 01 DHS?

No, a 1994 Cadillac DeVille's 4.9L engine (the Northstar V8 wasn't introduced until 1993 for the DeVille) will not fit in a 2001 DeVille DHS without significant, and likely impractical, modifications. While both are Cadillacs and even DeVille models, the chassis and engine bay are different enough between the 1994 and 2001 models to make this swap infeasible. The 2001 DHS uses a different generation of engine and likely has different mounts, wiring harnesses, and other components that are not compatible.