Working in the construction industry, I can tell you that MANY houses go up with exposed OSB subfloors. Typically, when the build the floor, the rains come in droves... The house can sit for about 2 weeks before they finally get the walls up, and another week before the roof gets sheathed...
The point is you have to let it dry out well after you're finished. You'll have no problems with it with a little rain... At most, some seams may pucker a little.