The voodoo cards couldn't do 2d.
When you played games that used the voodoo cards they would switch over the monitor cable from the pass through, so your 2d card wasn't being used at all.
I remember we had to do several tricks to do 2d on the voodoo.
One was to draw a plane and texture map the 2d image onto the plane, using alpha maps for transparency. Even simple things like the score display were done this way.
You could sometimes catch a glitch while playing where the plane the score readout was textured on would be visible for a second.