Is it possible to play Minecraft without any water in ocean biomes?
You can always install Singleplayer Commands, if that's still up-to-date, and use the
//drain command with a huge radius.
edit To obtain "oceans" without water, I think Terrain Control offers what you're looking for, and much more:
There's both a bukkit and a SSP version, and even better, if it doesn't achieve what you want, the source is hosted at github, so you can simply modify it!
If you want to get rid of the water in oceans: Mystcraft allows you to create different worlds, maybe if you create one without water symbols you get what you want, you can e.g. use Desert or Frozen Ozeans/Rivers.