I understand that vegetarians are against meat, and gelatin is derived from meat and bones. So the obvious answer is "no."
But I'm not entirely sure. What constitutes an ingredient as "vegetarian" or "vegan?"
Without further qualification, if someone refers to themselves as vegetarian (in America), the general assumption is that they are lacto-ovo vegetarian. That means they don't eat animal products that require killing the animal, but eggs and dairy are fine. Gelatin comes from a dead animal (unless they start harvesting it with arthroscopic probes :), so it is not a vegetarian ingredient. There are many other hydrocolloids, such as agar, that can be used to produce similar textures if needed.
Vegetarianism is not clearly defined, but a catch-all for various dietary choices.
Some vegetarians, will just simply not eat red meat, but would eat fish and poultry. Gelatin and Rennet (found in cheese) may or may not be included. I have friends who don't eat mammals, and others who won't eat anything warm-blooded.
Lacto-Ovo vegetarians will eat eggs and dairy, but not any muscular tissue. Again, Rennet and Gelatin are options they may or may not include.
Vegans, in the strictest sense, will not eat any animal flesh, nor will they eat animal derived products. In the purest sense, a vegan will exclude dairy and honey, but many vegans will include honey, and some will include dairy.
Those that choose vegetarianism for health reasons may break their diet occasionally for special occasions, such as a Thanksgiving turkey. Ethical (Animal Rights) Vegans, generally will not, and will question every ingredient.
Again, there are even ethical (environmental) vegetarians, who may be week-day vegans, and weekend Carnivores, finding that discipline easier to follow than simply reducing meat portion sizes. My boss, for example, is a Daytime Vegan, but once the sun goes down, he'll fire up the grill.
A good test for vegetarianism is to check the products for a KOSHER - Dairy symbol. If it can be served with dairy according to Kosher Rules, then it should be meat free.
EDIT: Other answer states the Kosher products may contain fish, so Kosher-Dairy only guarantees free from meat/poultry.
Gelatin is not vegetarian as it is made from dead animals... any vegetarian, from ovo-lacto in the liberal end to the fruitarian on the extreme end should have an aversion. A person who eats fish and/or poultry is by no means a vegetarian, just a selective omnivore.
If you need a similar product fruit pectin is a good alternative.
A product labeled kosher dairy will not automatically be okay for vegetarians. Kosher gelatin simply has been processed enough that the source is no longer identifiable -- it doesn't mean that it's not from a meat source to start with. Be careful to find out the rules for the particular kosher certification agency before relying on that.
Incidentally, unless the kosher certification specifically says that it's meat or dairy, the product is most likely pareve (the other category -- contains neither meat nor dairy, so can be eaten with either).
In addition, according to Ashkenazi (Eastern European Jewish) tradition, fish is not considered to be meat, but pareve. So if you avoid meat, kosher gelatin may still contain fish.
Gelatin is definitely not vegan. It is derived from collagen, a protein that connects bones, muscles & tendons. People often confuse it with Pectin. And it is also a common query that if pectin is vegan or not? This doubt arises because both are used for similar purpose.
Although for all those consuming vegan substances strictly, can opt for gelatin.