Delta Velorum - non-observed variable star
Yes it varies in the visible spectrum.
The paper  The nearby eclipsing stellar system δ Velorum describes why this is difficult target.  Surprisingly it is because it is so bright.
The absolute brightness of a star will vary significantly due to absorbtion in the atmosphere.  If the sky is slightly hazy, then the stars will be dimmer.  To measure the magnitude of a star, then, you don't directly measure how much light is coming from it, but compare it to nearby stars.  But δ Velorum is one of the brighter stars in the sky, so there are fewer nearby comparison stars.  This, combined with the long period of the orbit makes observations harder. This probably explains the shortage of observations.