So I did some basic testing to see how worthwhile the "Premium for Volunteers" event is, and how the different levels of bonus affected conscript numbers. I did three tests each at every level for both sides of the conflict.
Confederacy at 106 National Moral
No Bonus: Test 1 - 120 Conscripts, Test 2 - 150 Conscripts, Test 3 - 120 Conscripts
$1 Bonus: Test 1+2+3 - 150 Conscripts
$1.5 Bonus: Test 1+2+3 - 250 Conscripts
$2 Bonus: Test 1+2+3 - 375 Conscripts
Union at 88 National Moral
No Bonus: Test 1 - 250 Conscripts, Test 2 - 125 Conscripts, Test 3 - 250 Conscripts
$1 Bonus: Test 1+2+3 - 300 Conscripts
$1.5 Bonus: Test 1+2+3 - 500 Conscripts
$2 Bonus: Test 1+2+3 - 750 Conscripts
Before anyone asks, yes I did check to see if any other events popped up which affected conscript recruitment
I have no clue why selecting No Bonus gave me varied results while the other bonus levels did not. The text about national moral affecting recruitment, and implying some degree of random chance with the various bonus levels, does not actually seem to be correct, with the plausible exception of No Bonus. Although I did not do the math, presumably recruiting 750 conscripts at a $2 bonus with the Union costs $1500, while recruiting 375 conscripts with the Confederacy at a $2 bonus costs $750; so while the Union's bonuses do bring in twice the conscripts, they cost twice as much, meaning the question, "are they better", is not so clear cut.