In some of the Macs the seat is removable in some not. I know that all the new Macs have a removable seat. I have a 1999 Vogue and the seat comes off but I had a 2002 Quest and the seat didn't come off. Anyway, if you look how the seat attaches to the frame, you can tell if it's removable or not. It's obvious once you take a closer look.
The hood comes off the frame but it doesn't come off the hardware that is inside the hood. So you can't put it in the washer but you can always try to hose it down. If you get the seat off, you can put it in the washer on gentle cycle. I recommend that you line dry it.