I can’t give you a solid answer on that. I still have minor back troubles… and I haven’t been able to loosen up my hamstrings very consistantly.
During last track season I actually became decently flexible (about 3" past my heels on a sit and reach) But during that time, I wasn’t doing any squatting. Coincidentally, I also became a lot faster. I was the fastest I had ever been in my life. I find it very difficult to gain strength and flexiblity because Im sore a lot. Maybe thats just me.
I really haven’t found a way to stretch my lower back. It kind of rounds when i squat deep- probably the cause of my back problems. I haven’t found the pain or the soreness enough of a negative to outweigh the benefits of squatting, so I continue to squat heavy.