It can be done, but you have to be careful that the rooster doesn't over mate the hens. Over mating can be stressful on the hens and the hens and a good sign of it is loss of feathers on the neck and back.
Totally totally depends on the roo. My roo treats the one hen friend he has like a total princess and she knows it and revels in it. He is gentle and doesn't bother her in the least. Once in a blue moon they get close but she is okay with it and he never hurts her.
HOWEVER, when he was temporarily staying at another home with many hens but not allowed to free range like he was used to, he was not as happy nor as gentle. Even tho there were something like 25 hens and he was the only roo (at first there were a couple of others but they abused the girls so they were rehomed) he just wasn't all that happy.
Once this boy was back with one hen and given freedoms he resumed his prince-like qualities - any hen would think she died and went to heaven in his care.