Had a few argos over the years. Ran them in just about every condition. If your going to run a good motor you wont need to rely on the tires for forward momentum in the water, so you could choose a more aggressive tire. Keep in mind, they need to be the same diameter as the stock tires. They are a non standard size tire, so youll have to find the size and look for something based on size, not style (as in, dont just look for ATV tires).
You COULD also try as set of more aggressive tires only on the front (as long as the size was identical to the other 4 tires it will be fine) but like the others have said, argos are not known to "climb" out of low traction surfaces like water very well at all. With that said, if youve got a decent winch, you should be able to get yourself out of just about anything.
Our argos have always been new so taking on water has never been a problem but I have read and heard many stories just like the ones above in regards to the wheel bearings. One of the weak points of the argo in general.