No, previous versions rendered purely on the CPU. We did use the GPU on macOS to draw to the window itself, but actually rendering the frames was still done on the CPU.
Unless you're doing something graphically intensive you don't need a GPU at lower resolutions. At higher resolutions (or with much slower CPUs) you do need a GPU to keep up though.
I'm still using Sublime Text 2 on macOS Mojave and sometimes, but not always, if I take a screenshot of it, the text gets captured without syntax highlighting despite being highlighted on screen. So it's definitely doing some graphical shenanigans to render text as fast as it does.
Unless you're doing something graphically intensive you don't need a GPU at lower resolutions. At higher resolutions (or with much slower CPUs) you do need a GPU to keep up though.