For the benefit of those not familiar with "Old Hickory Knives," OKC stands for Ontario Knife Company which makes them.
The right bevel angle(s) for your cleaver depends to some extent on how you plan to use it, to an even greater extent on how you sharpen, and perhaps -- mostly -- to the thickness of the cleaver and how acute an angle you can actually sharpen. Old Hickorys have undergone some changes in the last few years, knife thicknesses are a lot more consistent, and usually thinner, but I just don't know for sure what's up with the cleavers.
Cleavers take a lot of abuse and often work best with some sort of multi-bevel. Assuming you're a freehand sharpener, try something like a 15* secondary bevel (the bevel between the cutting bevel and knife face) and a 22.5* primary (cutting) micro-bevel on top.
Just to make things clear, my angle numbers aren't a prescription to run out and get a digital angle finder. By 15* I mean as thin as as you can get without moving a substantial amount of metal and by 22.5* I mean holding the knife vertical to the stone, halving the angle to roughly 45*, then halving that to roughly 22.5*. The operative concepts -- especially with a tool as crude as a heavy cleaver -- are keeping things practical and understanding that "roughly" and "precisely" are different things.
If you can't get the knife much thinner than 20* just go with that rough and ready 22.5*. Bear in mind that we're talking about a cleaver and not eye-surgery scalpels.
The first part of maintaining a cleaver's edge is not something you do, but something you don't. Don't swing your cleaver like an axe. Put the edge where you want it to cleave, put your offhand along the cleaver's spine, and lean on the knife while rocking it slightly. If you use an ordinary board, hacking will wreck both the knife and your board.