Similarly compact, sort of the prototypes for the modern ATP forehand. The prep seems kinda similar to my eyes, both like to use rather open stances (but who doesn't these days).
On the 'no' side, the major grip also makes the rest of their swings markedly different. For one, Fed has a straight arm whereas as Kei's is substantially bent. This in turn affects the positioning and angles of their joints/levers, and also means that their strike zones will be very different, with Fed having his strike zone more in front of him.
But yes, I do like to think of Kei's forehand as sort of the bent-arm, westernish version of Fed's. And I think they are two of the best forehands to study: if you have a more conservative grip (semi-western and eastwards) then look at Fed, if you have a more extreme grip then look at Kei.
This is just a face analysis. I'm sure there are people who can go into more detail.
Federer forehand ... he's not turning through with his shoulders and hips ... he plants his leading foot, weight off the back foot ... and it's the arm that's doing the work (cause it doesn't take much cause it's a tennis ball, not a baseball). Have you ever practiced against a wall? It returns the ball at the same speed and doesn't turn its shoulders or hips one bit.