[/Devices/vga/0/Config/] (level 4)
3DEnabled <integer> = 0x0000000000000001 (1) <-- self-explanatory
...
VMSVGA3dEnabled <integer> = 0x0000000000000001 (1) <-- VMSVGA and VBoxSVGA
VMSVGAEnabled <integer> = 0x0000000000000001 (1) <-- VMSVGA and VBoxSVGA
VMSVGAPciId <integer> = 0x0000000000000001 (1) <-- VMSVGA only
Another clue is that in the VBoxVGA+3D case (the old, legacy one), something like the following would appear in the very beginning of the log, before the "CFGM dump" section. The following is from my 2015 MacBookPro11,5. Note the OpenGL version is 2.1, which is weird, because the MBP supports OpenGL 4.1 according to the OpenGL Extensions Viewer:
OpenGL: Offline rendering support is OFF (pid=9436)
OpenGL Info: 3D test passed
OpenGL: Offline rendering support is OFF (pid=9436)
OpenGL Info: Render SPU: GL_VENDOR: ATI Technologies Inc.
OpenGL Info: Render SPU: GL_RENDERER: AMD Radeon R9 M370X OpenGL Engine
OpenGL Info: Render SPU: GL_VERSION: 2.1 ATI-1.42.15
...
OpenGL Info: Render SPU: GL_MAX_VERTEX_UNIFORM_COMPONENTS_ARB=4096
OpenGL Info: Host supports version 2.1 [2.1 ATI-1.42.15]
OpenGL Info: Cfg: u32Caps(0x1f), fVisualBitsDefault(0x23)
Shared OpenGL service loaded -- 3D enabled
************************* CFGM dump *************************
With 6.0.0, using the VBoxSVGA or VMSVGA with 3D enabled, the host's GPU info appears right after the "CPUID dump" section:
******************** End of CPUID dump **********************
...
Changing the VM state from 'CREATED' to 'POWERING_ON'
VMSVGA3d: OpenGL version: 2.1 ATI-1.42.15
VMSVGA3d: OpenGL Vendor: ATI Technologies Inc.
VMSVGA3d: OpenGL Renderer: AMD Radeon R9 M370X OpenGL Engine
VMSVGA3d: OpenGL shader language version: 1.20
VMSVGA3d: OpenGL extensions (156):
...
VMSVGA3d: Alternative OpenGL version: 4.1 ATI-1.42.15
VMSVGA3d: Alternative OpenGL Vendor: ATI Technologies Inc.
VMSVGA3d: Alternative OpenGL Renderer: AMD Radeon R9 M370X OpenGL Engine
VMSVGA3d: Alternative OpenGL shader language version: 4.10
VMSVGA3d: Alternative OpenGL extensions (114):
...
Changing the VM state from 'POWERING_ON' to 'RUNNING'
Note that there are two versions of OpenGL showing; 2.1 which is the "Compatibility" one according to the OpenGL ExtViewer, and the "Alternative" 4.1 which is the "Core" according to the same program.
Hope it helps you figure out those logs a little bit easier...