I think if the teak wood is oven stabilized before making a gun and it is laminated construction, unless you hang it out in the sun like a salted fish, I sure hope it won't warp. Oiling sure keep the moisture content more or less stable.
The Olympic airgun also uses laminated wood for the stock, the manufacturer mentioned about stability. For these guns shooting error of 1-2 millimeters at 10 meters can mean a lost gold medal. The all weather hunting gun have been using Cycolac or Kevlar or whatever non woody for the stock to replace solid beech wood or walnut. Stock expansion in severe weather from solid wood have been known to cause accuracy error.
My house doors and frames are all teak, it is now 25 years old and have survived two major renovations plus a few big flood...:waterwork .. a few times. Teak is damn good, that's all I can say, but the price is getting horribly expensive.
However one thing I hate about wood guns even if they are teak, some area where I can't oil well seems to develop dark spot from too much use in water. Usually in the butt area. No strength loss but sure looks un-pretty.