No they are not.
A Commander uses the same frame as a full size 1911, except the barrel is 4.25" instead of 5". Most of these frames are not made of "lightweight" materials.
An Officers 1911 uses a smaller frame and is often made of lightweight materials.
Now, for example, a Compact 1911 can be an Officers frame with a compact slide on top of it, such as the one that goes with a 3.5" barrel. (This gun is prohibited due to the barrel length, but is the lightest, smallest and most easily carried and concealed).
A hybrid Compact, if you will, uses the Officers frame with a full size Commander slide and barrel riding on it (4.25") and is restricted, not prohib.
A visual example can be seen on the Dan Wesson website at
www.cz-usa.com - compare the two bobtail .45s they offer. The stainless vs. the black one. Notice the differences on the frames, including the lighter weight and smaller handle size on the black one.
I hope this clears it up!