My dad is trying to purchase a property adjacent to his to clear use for a horse pasture and to keep bad neighbors away. The property he is interested in is a small parcel and is in a flood zone and the creek routinely floods the property during certain times of the year. My father knows this and is fine with it since he can move the horse to higher ground when it happens.

This particular property is bank owned as it was taken from the previous owner based on insurance fraud. Since the auction, I looked on the site and noticed there is no notice or disclosure that the property is in in a flood zone. Is it not required by law that they disclose that the property is in a flood zone? I've done some research and it appears that it is required when it is single family residential property. This is residential, not commercial. There is no dwelling on the property so I don't know if that is their legal loophole or if they are just intentionally withholding the information. This auction is also online and the realtor/bank are out of state so I don't know if that could also be a legal loophole for them.

There have been numerous other shady things about the listing and we suspect their was a shadow bidder trying to drive the price up during the first auction. As said before, we know it is in a flood zone and don't care. But I think it is highly unethical for them to be posting and auctioning the property without disclosure.

It comes out in title

Not for auctions, no.

Your first mistake was in thinking that anything in the listing is going to be honest or accurate.  This is even more so when dealing with a bank owned property.  Someone in an office somewhere pushed some papers.  No one has verified anything on the papers or at the property.  

You can find the flood plane maps online.  They just expanded the size of the flood planes as well.  The area on my property that creek runs through had the flood plane area increased by about 1/3.