That’s a very low percentage of Union soldiers who were drafted or paid substitutes.
From www.civilwarhome.com:
Conscription (Military Draft) In The Civil War
There was no general military draft in America until the Civil War. The Confederacy passed its first of 3 conscription acts 16 April 1862, and scarcely a year later the Union began conscripting men. Government officials plagued with manpower shortages regarded drafting as the only means of sustaining an effective army and hoped it would spur voluntary enlistments.
But compulsory service embittered the public, who considered it an infringement on individual free will and personal liberty and feared it would concentrate arbitrary power in the military. Believing with some justification that unwilling soldiers made poor fighting men, volunteer soldiers despised conscripts. Conscription also undercut morale, as soldiers complained that it compromised voluntary enlistments and appeared as an act of desperation in the face of repeated military defeats.
Conscription nurtured substitutes, bounty-jumping, and desertion. Charges of class discrimination were leveled against both Confederate and Union draft laws since exemption and commutation clauses allowed propertied men to avoid service, thus laying the burden on immigrants and men with few resources. Occupational, only-son, and medical exemptions created many loopholes in the laws. Doctors certified healthy men unfit for duty, while some physically or mentally deficient conscripts went to the front after sham examinations. Enforcement presented obstacles of its own; many conscripts simply failed to report for duty. Several states challenged the draft's legality, trying to block it and arguing over the quota system. Unpopular, unwieldy, and unfair, conscription raised more discontent than soldiers.
Under the Union draft act men faced the possibility of conscription in July 1863 and in Mar., July, and Dec. 1864. Draft riots ensued, notably in New York in 1863. Of the 249,259 18-to-35-year-old men whose names were drawn, only about 6% served, the rest paying commutation or hiring a substitute.
The first Confederate conscription law also applied to men between 18 and 35, providing for substitution (repealed Dec. 1863) and exemptions. A revision, approved 27 Sept. 1862, raised the age to 45; 5 days later the legislators passed the expanded Exemption Act. The Conscription Act of Feb. 1864 called all men between 1 7 and 50. Conscripts accounted for one-fourth to one-third of the Confederate armies east of the Mississippi between Apr. 1864 and early 1865.
Source: "Historical Times Encyclopedia of the Civil War" Edited by Patricia L. FaustThis Page last updated 02/15/02