White smoke or steam is normal from the exhaust port as it exits the boat at the back of the hull, since Seadoo's (and most all boats) cool the exhaust by injecting water into the hot exhaust gas just downstream from the manifold. This injected water then ends up as steam as it goes out the back of the boat. White steam smoke with no distinguishing smell, is normal. Blue/grey smoke would be bad (4-tecs only), or if it had a sweet smell could mean engine oil or coolant consumption.
Now for as where you see smoke coming out right at the mating surface between the manifold and the exhaust pipe, this is not normal. It could be that some light oil is burning off the hot exhaust system from when the engine was winterized (When you winterize the engine you are supposed to spray they engine with a fogging oil or wd-40 to protect from moisture). If it goes away, then I would not worry about it. If smoke from this gasket area continues then it sounds like some sort of leak and/or a bad gasket.
Poke around in there and make sure that all the clamps and screws of the gasket are tight (not sure off hand how everything is held together), you can view an exploded diagram from the exhaust system by clicking the 'parts' link at the top of the forum and it may help understand how everything mates together.
Hopefully it is something simple like loose clamps or maybe even a bad gasket, and not something serious like a cracked manifold which could happen if it froze and was not winterized properly. In any event this is kind of rare and I have not heard of this problem before. This is all that I can propose at the moment, but maybe others will have better theories. Hope it helps, and let us know what you find. Good luck!