People do it all the time. It doesn't change the space requirements -- although things will be more peaceful if they have a back ard or field to range. One will be dominant over the other, and will do most of the mating and crowing. The non dominant one will try to se=neak in some mating when the dominant one isn't looking.
Of course, first they have to decide who is dominant. This may not involve anything more than a little chest bumping. or it may involve some serious fights. I've kept only dual purpose birds and have never seen a serious fight -- but chickens are individuals.
Help we have a chicken that is acting weird don't know what's wrong or what to do. She just lays around not even interested in eating. Anyone know what to do for her?