Maybe in the east. What I have been reading recently from Union soldiers in the west tells another story. E.g., Private Daniel Ambrose of the 7th Illinois Volunteers in tomorrow's diary entry.
"The troops still continue foraging, and in consequence the country has well nigh become impoverished, almost everything in the line of subsistence having been confiscated. But occasionally a hog, goose, or chicken ventures from some hiding place and falls a prey to the 'inveterate Yankees.'"
For sure there were some, most notably Grant's Vicksburg campaign, final stages, and Sherman's March to the sea.
But no way to quantify those to say, for example, "the Union Army lived on its own resources 85% of the time and lived off the land only 15%, While for Confederates it was the reverse."
We don't know, we can't say anything like that.
But I'd guess the real numbers are somewhere near those, based on everything I've read about the Confederate army and the Union's dependency on its own supply lines.