A.C.
I can't answer for sure with the newer models, but I have 2007 Odyssey, and NO, the middle jump seat is not approved for car seats in our car. You can find the answer to this question in the car manual, (and often in the carseat manual as well) so ask the dealer to let you see the manual the next time you go to look at cars.
What we have done is removed the jump-seat completely and spaced the right-hand bucket seat over to the middle. This allows for easy access to the back row of seats from the door, so perhaps your son could go back there, as well as one seat in the middle, but it does not allow for three seats across in the middle.
I love our Odyssey, though. The biggest difference between the Odyssey and the Sienna is how the van handles, so make sure you test-drive one of each and get a feel for which style you prefer.