I don't think there is one right answer here.
Do you "need to"? well, you "are" giving a gift - a very special gift, worth probably more $$ than whatever gift you were going to give. A videographer costs a lot of money, plus - this will mean that during the important parts of the wedding you will be working and not just sitting and enjoying. IMHO that is a huge gift.
"Should" you give a gift? that depends on your relationship, your finances, etc.
It's hard to say what would i do - for example, when i got married (second wedding) my sister flew many many miles to be with us and she didn't give a gift which was totally fine with me - having her at the wedding was worth so much more to me. And she didn't work at the wedding, she was just there. If i were in your shoes, i would think that the work/dvd is my gift.