You’d need to have a more detailed breakdown of the 1860 census to be able to calculate how that 5% compares with the total military age cohort. There may be one available with enough digging.
The stats are out there, but I don’t feel like doing that digging right right now. I’ll just end by saying that a rebellion by 179,000 slaves would be considered a pretty big deal, given that Nat Turner’s Rebellion, which spread horror throughout the south, involved less than a hundred.