I don’t know that there is a particular brand or model of washer that is best suited for horse blankets and pet betting, however, having large washers (I would say 60lb+) would be important. In terms of maintenance or modifications, the only thing I’m aware of is that the drums can have residual hair/fun in them. Having either a staff person cleaning out the drums after each use, or having materials to let customers wipe out and spray down the drums before use would be helpful. Also, the drains should be inspected and cleaned more often.
Someone else might have more insight but just thought I’d add my 2 cents.