Yes, you can wholesale a house under foreclosure. The owner still owns it and can sell it until the foreclosure process completes and they are no longer the owner. The house needs to be at a wholesale price, though, which will likely involve a short sale. If the owner is motivated and in foreclosure, they probably don't have equity because if they did, they would just sell the house to avoid foreclosure.
Just use the 70% rule. If you can wholesale it without doing a short sale, great. If not, find an investor or an agent in your area who is experienced in doing short sales and work out a win/win/win agreement for the homeowner, you, and the person with short sale experience.
If the house has been foreclosed on and bank-owned (REO), you can absolutely wholesale. Simply present the offer to the listing agent who will give to the asset manager for approval. Once you have an executed contract you can look for a buyer to double close (banks won't allow assignments). Just make sure you read the addendum thoroughly to ensure there aren't any deed restrictions.
If the owner is in pre-foreclosure, you can still contract and wholesale before it goes to auction. If the homeowner doesn't have enough equity in the property (which is common - they owe the lender more than your offer price), you'll need to work out a short sale. You can still wholesale these deals, but again, just look out for those deed restrictions - they are more common with short sales and can even be more strict.
In my opinion, REO's are simpler, faster, and easier to get done but the profits (especially in my market ) are typically smaller.
Short Sales are typically a pain - they take a lot of investment, time, patience, paperwork, creativity (i.e. to get around restrictions), but the payoff is generally greater. I have a short sale now that I've been working on since early October of 2015. We are closing on 3/18/16 :)