Many slaves were loyal to their owners, including the slaves of my ancestors. Our slaves buried the family silver to protect it when Sherman's men came by. So my grandmother told me. Her mother, who was there when it happened, told her.
There was fear in the South that slaves would revolt. But with the white men gone fighting the war, most slaves just continued toiling in the fields and gardens for themselves and the families that owned them. They could have revolted en masse, but they didn't. However, when Northern troops arrived, many slaves would often leave the farm. Who wouldn't want to be free? That's not to say that all Northern troops were kind to slaves. Northern troops did plunder slave cabins and abuse the slaves too just as they had done with the whites.
In Texas in the summer of 1860, many towns and farm buildings were burned, purportedly set by slaves and abolitionists. This was known as the "Texas Troubles." Slaves from hundreds of miles apart testified to the same basic plot of white guys (abolitionists) encouraging them to set the fires. These incidents sound much like the abolitionist circular described in Congress that I posted above.
The anti-Breckenridge party dismissed the fires as paranoia resulting from matches self igniting in an exceptionally hot Texas summer. They argued that the newspapers were stirring up the paranoia to induce people to vote for Breckenridge. The Breckenridge folks felt that the fires were incited by and lit in some cases by abolitionists and cited tests where thermometer heat was not able to ignite the matches.
Here is an old post that lists some of the fires. [fires]
There surely were many such situations of fraternal feelings, but there had to be a general southern recognition that the slaves' overall situation was terrible or revolution would not have been such a broad southern fear. After all, if the Confederate mindset was willing to risk a Civil War over the election of Lincoln, why wouldn't other men be expected to revolt against bondage? I guess that's one reason the rebs wished to separate secession and revolution