My guess would be that they were probably conscripts. However, it's almost impossible to tell if soldiers who joined the army after the passage of the Conscription Act were volunteers or conscripts. Most muster rolls made no distinction, and prisoner of war records are no help -- many POWs claimed to be conscripts (possibly in hopes that it would get them released faster), including men who claimed to have been conscripted against their will in May and June of 1861.

Most of those militiamen who I can positively identify, and didn't go on to serve in the Confederate army, were over the age limit of the Conscription Act.