As far as I know, no source engine game can actually run on Direct3D 8. Games can run in dxlevel 80 mode, which is like a compatibility mode for GPUs made for DX8 that technically support DX9 but not very well, but it still always uses the DirectX 9 API.
Vampire: The Masquerade - Bloodlines may be an exception as it's on the oldest version of the source engine (but I haven't checked).
Otherwise I would suggest that these games be removed from the list unless someone can demonstrate a source engine game actually running with D3D8.