questionsdo i need to hook up my dvd if i have a bp620…

vote-for0vote-against
vote-for5vote-against

no. bluray players will also play dvds.

vote-for1vote-against

Your Blu-ray player will likely upconvert the SD DVD material to an HD resolution. If you prefer this look to that which your DVD player provides, there is no real need for you to connect the DVD player.

The only exception here would be if your DVD player supported a format which your Blu-ray player did not. Looking at the specs for the LG-BP620, the following disc formats are supported:
BD-ROM, BD-R, BD-RE, DVD (NTSC), DVD (PAL), DVD-R, DVD-RW, DVD+R, DVD+RW, Audio CD, DTS-CD, CD-R/CD-RW
...The only non-supported formats that stand out to me are DVD-A and SACD. Both are high-fidelity audio formats and chances are high you would know if you had anything in either format.