Yes, if you’re talking about rendering 2D using SDL’s built-in renderers, it would need to use the OpenGL renderer as there’s no support for blitting pixels directly to a GBM surface. In theory, the driver could choose between creating KMS “dumb buffers” which can be blitted to, or GBM surfaces which can be drawn to using EGL + OpenGL, but right now it only creates a GBM surface and so can only support rendering using EGL + OpenGL.
It was originally based on the Raspberry Pi dispmanx driver which has the same approach & limitations.