Not saying it won't happen, but you might be surprised what the appraiser will say in his report. I recently bought a REO that had similar issues. The concrete driveway was broken up and the slab had tilted toward the house. Any rain from the front half of the house would end up emptying right at the foundation of the house. The water had soaked into the house and caused mold/mildew to start in the crawlspace on this tri-level house.
I fully expected the appraiser to point this out in their report, but they just noted the dampness and stated it smelled somewhat musty and that it was normal for a house in this area.
In my estimated repairs list that I turned into the bank, I included a line for mold remediation. My loan officer called me after he got the appraisal and told me that since the appraiser didn't mention it, I should remove that line and hide that cost in another line item. He said that would give me the best chance for underwriting to ok the loan.
So, just because you see it (and Ray Charles could see it), doesn't mean that it will be noted in the appraisal.