Yes, some truth. It hastened the costly and deadly war which was good because the North was growing weary of war. So was the South , but they had no choice to continue on .
I'm not sure what the north made of the situation. You've got tens of thousands of men, formerly slaves, who are not properly trained as soldiers. Give them guns and that's a risky proposition I think. However, the former slaves relished the opportunity to get in the fight and take it to their oppressors. They fought valiantly, and when they were captured, they met a horrific end to their lives through torture and other cruel methods of execution.
The North had a problem where by former slaves, men, women, children, and elderly followed their camp from battle to battle as they were freed. They saw safety in the shadow of the North's Army. However, they were also a burden to the Army, because they slowed it down and they themselves needed resources to live which hindered those available to the Army. Lincoln emancipating the slaves was a brilliant move. The war had slavery as its main theme, but trumping at I think was Lincolns desire to to keep the union together. It wasn't apparent immediately, but Lincoln and the north realized that the issue of slavery had to be dealt with decisively. No more compromises on it. All or nothing.