I'm not sure where the pumps are located on your boat, but you shouldn't have to remove the pumps to check them. To your second question, yes the impellars are replaceable. On my boat they are located in the back of the engine compartment above the engine (03 MB Sports 220V).
Here is a picture of one of them.
Just remove the for little screws on the plate at the bottom and you'll see the impellar.
(Message edited by moon on May 22, 2009)