Does your Rex actually have sore hocks now ? If so has he/she been seen by a Vet? As explained in a previous post, it is important to ascertain if there are any other contributory factors to the problem other than breed predisposition.
Some Rabbits will not tolerate wearing any dressings/socks and will simply chew them off. This can cause even more potentially serious problems should they ingest fabric. So before spending your money on buying ‘hock socks’ I would first discuss options with using bandaging with a Rabbit savvy Vet. The Vet could show you how to correctly apply the bandage with an anti- pressure dressing under it. Rather like a large corn plaster which takes direct weight-bearing pressure off the sore area.
What topical treatments to use on sore hocks depends on the severity of the problem. Sometimes systemic medication is needed too, especially anti inflammatory analgesia. This can only be obtained via a Vet. If the hocks are infected systemic antibiotics are needed too.
The best source of qualified information and advice about treatment options is a consultation with a Rabbit savvy Vet.
Its obvious you are being very responsible and trying your best to make sure your Rex has the appropriate care

I think the best thing to do is to make sure you consult a rabbit Savvy Vet who can give you individualised advice about what treatments are needed depending on the findings of a thorough examination.
I am sure your research has already informed you that there are basic things we can do to try to minimise the development of sore hocks - ie making sure the Rabbit’s toe nails are clipped to the correct length, providing a suitable substrate which is always clean and dry, making sure the Rabbit does not become overweight and not keeping them confined to a hutch/cage so they have plenty of room to exercise, not just spend all day loafed in one place.
With the Rex predisposition to sore hocks, in my 28 years experience of caring for the breed, if they get to a year of age with no fur thinning over the hocks as long as they are always housed appropriately, not allowed to get overweight (a big challenge, Rexes are exceptionally greedy!) and their nails are kept trimmed to the correct length they are no more likely to get sore hocks than any other breed. The genetic predisposition always becomes apparent in the first year of life. It can be very disheartening to see when we know all precautions to avoid it have been taken.