Might post a pic of the knife, or specify the make/brand & model of the Santoku. If it's a high-dollar or specialty or custom knife in an exotic steel, you might wait for more suggestions on a better sharpening method, aside from using the Chef's Choice sharpener.
I'd think the hollow grind shouldn't matter much, if at all; 15° per side should be safe for it, as for most knives. Again, if it's a special grind (such as asymmetrical edge grinds found on some Japanese knives), specifying the maker and including pics would be a good idea. The Chef's Choice sharpener may not be the best option for blades with specialty grinds. If it's just an inexpensive store-bought kitchen knife in a mainstream pattern, there shouldn't be any worries in using the Chef's Choice.
David