Body language is absolutely an important part of etiquette. People can convey as much meaning (or more) with their bodies as they can with their words. Therefore, body language is an important part of etiquette as the wrong body language can offend people.
An important part of etiquette is making people feel comfortable. Body language can be a big part of this. A person who uses intrusive body language can make us feel very uncomfortable. For example, a person who leans too close to us or who touches us excessively can seem very rude regardless of what they are saying verbally.
Another important part of etiquette is making people feel as if you are paying attention to them. Body language can be important here as well. We can be very insulting if someone is talking to us and we do things that do not indicate that we are attending to what they say. For example, if we look away from them constantly or if we fidget a great deal, we can make them feel as if we do not care about what they have to say.
In these ways, body language can be a very important part of etiquette.