Can bluray read dvd

In most cases - Yes.
I have 2 blu-ray writers in too desktop computers. They will write to and play Blu-ray, DVDs and CD,
I have two Blu-ray Rom drives in my two laptops. The both play blu-ray (do NOT write to) and they also play DVDs and can write to DVD-R, +R, +RW and to CD-r and RWs.

Most stand-alone units mimic the internal computer drives, just more expensive.
Normally the specs will list all the media that it can play and what media it can write to.