In constructing a composite or laminated bow, horn has a practical purpose.
A thin layer of horn is glued onto what will be the belly of the bow, the side facing the archer. Water buffalo horn is very suitable, as is horn of several antelopes such as gemsbok, oryx, ibex, and that of Hungarian grey cattle. Goat and sheep horn can also be used. Most forms of cow horn are not suitable, as they soon delaminate with use. The horn can store more energy than wood in compression.
In this alternate scenario, the horn of one other animal is being used in the process--that of the rhinoceros. The only problem is that rhino horn does not have a bony core--it's nothing more than compressed hair. So the question is: Would rhino horn be a feasible ingredient in the construction of a composite bow?