In my opinion....yes!
First, why would so many instructors put out nice instructional DVDs for the general public if they didn't think people could learn from them? Why would people put out youtube videos with detailed explanations if they didn't think people would learn from them?
Second, someone with a good foundation in any martial art should be able to learn something new from video. An absolute newbie that has done nothing martial arts related in the past is likely to have more trouble, but as long as he or she has any physical talent at all they should be able to benefit.
Third, plenty of people have learned that have had limited exposure to the instructor. Maybe they travel or the instructor travels and they received one on one instruction sporadically. Now imagine you had video of those lessons that you could refer back to at will! That is essentially what DVD instruction amounts to.
Granted, nothing beats hands on instruction! At some point the person learning from DVD will have to seek out an instructor for some quality training. But his or her feet should already be firmly on the path compared to someone with no previous exposure at all.
You are not going to learn advanced material very well from a DVD. But most DVDs don't contain the system's advanced material anyway!
If you are already studying a specific martial art, then having instructional DVDs is great to help you remember things and review things multiple times, maybe pick up on things you missed in class, maybe see how a different instructor from your same system explains and does things a little differently, etc.
If you are interested in a specific martial art but don't have an instructor in your area, then DVD can help you decide if this is really what you want to learn prior to traveling some distance to the school you are interested in. But you have to have a partner. Martial arts do not work well when only practiced solo! So grab a friend that is also interested and start working through the instruction on the DVD a little at a time. And have fun! That's the important part!