It might be sore hocks but it is hard to say at what stage they are: if they are dry and not infected scabs, he should heal up, as long as the flooring that caused them is removed. About the urine-stained bottom — what is his litterbox setup like? He should not have urine stains, he might need to be checked for a urinary tract infection if the litterbox is not to blame for this, i.e. if the box is not very wet so to stain his bottom.

Poor bunny! Ringo is a mini rex and that soft rexy fur made him susceptible to sore hocks too! He had minor sore hocks when I first adopted him and they proceeded to get worse for a while, very scary. I will try to find and upload pics I have of his poor hocks at their very worst! They have gotten much better now, but it is still a pretty serious ailment so your friend should make a vet appointment with a good rabbit doctor asap!

If the scabs are light pink that’s normal. When they get red or inflamed they need treatment.

I think with two issues combined it is wise to have him checked out by a vet. Be sure to describe the habitat to the vet, in case there needs to be a change to the set up. My mini rex had sensitive hocks as most do, and he wouldn’t venture onto anything but low pile carpet, so you never know what will work.